抄録
The mechanism by which cracks occur in the immersion nozzle with silicaless inner porous refractory developed to stabilize the injection of argon gas into molten steel, and the prevention of nozzle cracking were investigated. The results obtained were as follows.
(1) Models for estimating the crack formation pressure and hot argon gas inlet pressure for the immersion nozzle were proposed. Using those models, a theory for preventing nozzle cracking according to casting conditions was worked out.
(2) With the immersion nozzle with silicaless inner porous refractory, the hot argon gas inlet pressure does not drop. Therefore, when the initial gas inlet pressure is substantially high, a longitudinal crack tends to occur easily in the powder line which deteriorates in strength due to in the latter half of casting operation.
(3) By increasing the immersion nozzle wall thickness to improve its strength and controlling the hot argon gas inlet pressure below the crack formation pressure, it is possible to prevent cracks in the immersion nozzle with silicaless inner porous refractory.
