The immersion nozzle is to lengthen the tundish nozzle and insert it to a certain depth below the molten steel surface of the mold, which seals the pouring flow. The advantage of using the immersion nozzle is that it isolates the contact between the injection stream and the air, prevents the injection stream from splashing on the molten steel surface, and prevents secondary oxidation. Through the choice of nozzle shape, the flow state of molten steel in the mold can be adjusted to promote the separation of inclusions and improve the quality of steel. It can be said that the mold is poured with immersion nozzle mold slag, which has brought epoch-making progress to the development of continuous casting technology. The shape of the immersion nozzle mainly refers to the angle of the steel outlet. Generally, there are four types: straight hole type, side hole up, side hole down and box type. Which one to choose depends on the pouring speed and the cross-sectional size of the mold. It is generally believed that the immersion nozzle mold flux technology is only suitable for continuous casting of blooms and slabs, and for billets smaller than 150×150 mm, due to the small cross-section, the size of the immersion nozzle is limited. Large fluctuations may cause slag entrapment, so it is difficult to use this method.