PREVENTION OF CRACKS IN GAS INJECTION TYP E IMMERSION NOZZLE

The mechanism by which cracks are occurred in the immersion nozzle wit h silicaless inner porous refractory developed to stabilize the inject ion of argon gas into molten steel, and the prevention of nozzle crack ing have been investigated. The results obtained are as follows. (1) M odels for estimating the crack formation pressure and hot argon gas pr essure for the immersion nozzle were proposed. Using those models, a t heory for preventing nozzle cracking according to casting conditions w as worked out. (2) With the immersion nozzle with silicaless inner por ous refractory, the hot argon gas pressure did not drop. Therefore, wh en the initial argon gas pressure is substantially high, a longitudina l crack tends to occur easily in the powder line which deteriorates in strength due to corrosion in the latter hall oi casting operation. (3 ) By increasing the immersion nozzle wall thickness to improve its str ength and controlling the hot argon gas pressure below the crack forma tion pressure, it is possible to prevent cracks in the immersion nozzl e with silicaless inner porous refractory.