IMPROVEMENT OF LIFE OF IMMERSION NOZZLE WITH GAS-INJECTION

The mechanism by which cracks occur in the immersion nozzle with silic aless inner porous refractory developed to stabilize the injection of argon gas into molten steel, and the prevention of nozzle cracking wer e investigated. The results obtained were as follows. (1) Models for e stimating the crack formation pressure and hot argon gas inlet pressur e for the immersion nozzle were proposed. Using those models, a theory for preventing nozzle cracking according to casting conditions was wo rked out. (2) With the immersion nozzle with silicaless inner porous r efractory, the hot argon gas inlet pressure does not drop. Therefore, when the initial gas inlet pressure is substantially high, a longitudi nal crack tends to occur easily in the powder line which deteriorates in strength due to in the latter half of casting operation. (3) By inc reasing the immersion nozzle wall thickness to improve its strength an d controlling the hot argon gas inlet pressure below the crack formati on pressure, it is possible to prevent cracks in the immersion nozzle with silicaless inner porous refractory.