EFFECT OF COMPOSITION OF IMMERSION NOZZLE ON OCCURRENCE OF BLISTER INSTEEL SHEET

The effect of the inner porous refractories-molten steel reaction on t he incidence. of blisters and the mechanism whereby the incidence of b listers is prevented by using an immersion nozzle with a silicaless in ner porous refractories that does not react with the molten steel were studied. The following results were obtained: (1) Blisters are caused by 0.5 mm and larger argon gas bubbles, and particularly 1.0 mm and l arger argon gas bubbles have a strong bearing on the incidence of blis ters in the sheet product. (2) The mechanism whereby the incidence of blisters depends on the number of sequence cast heats can be explained by the increase in argon gas bubble diameter caused by the inner poro us refractories-molten steel reaction in the later heats in the sequen ce cast. (3) Fine argon gas bubbles can be stably introduced into the molten steel by using an immersion nozzle with a silicaless inner poro us refractories that does not react with the molten steel. This stable injection of fine argon gas bubbles helps prevent the occurrence of b listers in the sheet product.