MECHANISM OF FINE BUBBLES ENTRAPMENT BENE ATH THE SURFACE OF CONTINUOUSLY CAST SLABS

Origin of fine bubbles beneath the surface of continuously cast slab h as been verified. In addition, the influence of fluid flow condition i n mold on entrapment of the bubbles beneath meniscus has been investig ated through a simulation experiment with water models. The results ar e summarized as follows. (1) The gases compositions in the bubbles wer e N-2, Ar, H-2 and CH4, and the origin of each composition was air lea kage, Ar gas injected at slide gate, diffusive hydrogen in molten stee l, and coal-tar pitch soaked in refractorv of slide gale respectively. (2) Air leakage at the slide gate increased with passage of casting t ime, and the volume of leakage was estimated to be 100 similar to 550N cm(3)/s. (3) The size of bubble contained N, gas was smaller than that contained Ar gas and found in mainly center of slab width direction. (4) The distribution of bubbles existence in slab width direction depe nded on bubble size and molten steel flow beneath meniscus. (5) An app lication of the airtight slide gate reduced the number of bubbles bene ath the slab surface in the middle of width direction.