The formation of subcutaneous bubbles in continuous casting billets is mainly related to the following factors:
Steel absorbs external gases and water vapor:
External gases: including air, protective gases, etc. These gases enter the steel through equipment leakage, alloying, LF power supply, large overturning of wire feeding steel, open continuous casting or gaps in protective casting devices.
External water vapor: including leakage of converters and refining equipment, excessive moisture content of materials such as alloys, slag, protective slag and covering agents, insufficient capacity of the secondary cooling fan of the continuous casting machine, steam escaping from the crystallizer cover, poor baking of refractory materials such as tundish, etc.
Poor deoxidation of molten steel:
Poor deoxidation will increase the oxygen content in steel and form CO bubbles. After these bubbles are formed in steel, if they fail to escape from the surface of the billet, subcutaneous bubbles will be formed.
Moisture problem of protective slag and covering agent:
Excessive moisture content of protective slag and covering agent will cause molten steel to absorb moisture at high temperature to form water vapor, and then form hydrogen bubbles in steel, which may form subcutaneous bubbles during the solidification process of molten steel.
Equipment and maintenance issues:
Problems such as equipment leakage and poor baking of refractory materials can cause molten steel to contact with water vapor and form subcutaneous bubbles. In addition, problems with the water cooling system during continuous casting may also cause water vapor to condense into water droplets on the lower surface of the upper cover plate of the crystallizer, thereby forming subcutaneous bubbles.
In order to reduce the formation of subcutaneous bubbles in continuous casting billets, the following measures can be taken:
Strictly control the moisture content of raw materials such as protective slag and covering agent to ensure that they meet the specified standards.
Adjust the argon flow rate for continuous casting protection pouring to avoid excessive or too small flow to reduce the generation of bubbles.
Optimize the crystallizer flow field to reduce the bubble capture rate, such as appropriately reducing the billet drawing speed or optimizing the structure of the crystallizer submerged nozzle.
Strengthen material management to avoid material moisture, especially when operating in humid weather or environment.
Through these measures, the formation of subcutaneous bubbles in continuous casting billets can be effectively controlled and reduced, thereby improving the overall quality and production efficiency of continuous casting billets.
