Trials for reducing depth of oscillation marks in continuous casting

Improvement of surface defects in a continuously cast slab or billet is important for saving surface scarfing and for carrying out direct rolling. Deep oscillation marks, one type of the surface defects, sometimes cause surface cracking and positive segregation. In this study, the mechanism by which oscillation marks are formed was investigated by using a continuously cast simulator, which is a billet-type machine. Then attempts were made to reduce the depth of oscillation marks by two methods in which electromagnetic force, which is the most effective means for reducing depth, was hot used. The two methods were use of an adiabatic board for preventing solidification of a meniscus and the use of a board for suppressing the flow of flux. Overlapping of a molten metal on a meniscus resulted in formation of oscillation marks in tin. On the other hand, bending of a solidified shell also resulted in formation of oscillation marks in a tin-lead alloy. The depth of the oscillation marks formed by the overlapping mechanism was greater than that formed by the bending mechanism. Both mechanisms depended on the strength of the solidified shell. Therefore, two trials to reduce the depth of oscillation marks formed by the overlapping mechanism were carried out: In one trial, an adiabatic board was inserted into the molten metal. Reduction in depth of the oscillation marks reduced up to about 86% was:achieved when high viscosity flux was used. However, the adiabatic board was not effective when low viscosity flux was used. In the other trial; a board was inserted into a molten flux layer with a depth of 10 mm in depth in order to suppress the flow of the flux and to change the direction of flux flow, and the depth of oscillation marks was reduced by about 33%. Therefore, both of these methods are, effective for reducing the depth of oscillation marks in a continuously cast billet.