Abstract
Large non-metallic inclusions in the slabs casted continuously by the bow-type machine accumulated within the upper part of slab, that is, the inside radius part of casting machine. Most of such non-metallic inclusions were caused mainly by the erosion of tundish immersion nozzle and by the reoxidation of molten steel secondly. The characteristic accumulation of large non-metallic inclusions were caused by the inclination of the upper shell of steel from the vertical during casting and these phenomena were explained theoretically. Therefore, the bow-type machine had the disadvantage of trapping large non-metallic inclusions compared with the vertical type and the vertical type with bending.
In order to decrease the input of non-metallic inclusions, the following precautions are necessary;
a) Sealing of molten steel stream with Ar gas from ladle to tundish
b) Right selection of temperature and composition of molten steel, in the case of using tundish immersion nozzle made of fused silica.
c) Selection of material of tundish immersion nozzle which excels in antierosion to molten steel.
In order to remove large non-metallic inclusions as much as possible, the following measures are important;
d) The slow speed of molten steel stream at the outlet of tundish immersion nozzle.
e) Selection of the shape of tundish immersion nozzle advantageous to accomplish the good floatation of inclusions in molten steel.
