The influence of mold behavior on the production of continuously cast steel billets

Abstract

The origins of rhomboidity, longitudinal corner cracks, and breakouts in the continuous casting of steel billets have been investigated with the aid of heat flow and stress analyses of the mold wall. It has been shown that these problems can be linked to intermittent boiling in the cooling water channel, which may occur asynchronously on different faces of the mold. A mechanism based on asynchronous, intermittent boiling and nonsymmetrical cooling of the mold wall has been formulated which explains the influence of billet size, cooling-water velocity, water pressure, cold face roughness, and steel carbon content on the formation of rhomboidity and longitudinal corner cracks. Prevention of intermittent boiling is thereby shown to be a key factor in the production of defect-free billets. This can be accomplished by raising cooling water velocity, increasing mold wall thickness, increasing water back pressure, or roughening the cold face near the meniscus. These measures should also be effective in reducing the frequency of breakouts beneath the mold.