The formation of longitudinal off-corner depressions or "gutters" in continuous-cast steel slabs has been investigated using coupled finite-element models. Thermal-mechanical behavior of the solidifying shell has been simulated as it moves down through the mold and upper support rolls in the spray chamber. The calculation includes solidification, intermittent gap formation, plastic creep, bulging due to ferrostatic pressure, interaction with the mold and rolls, and phase transformations. The effects of turbulent flow in the liquid pool, flow and melting of the powder layers, superheat dissipation, taper, and thermal distortion of the mold walls are accounted for using separate models. Together, these models illustrate a multi-stage mechanism for gutter formation. The problem starts with a hot, thin region down the off-corner wide face. This may be caused by locally-inadequate liquid powder feeding, or by insufficient taper of the upper portion of the narrow face mold walls, allowing corner rotation within the mold. Depressions may then be created by excessive taper, buckling the thin shell near mold exit. Alternatively, they may evolve during bulging between support rolls below the mold, due to bending of the thin off-corner region. The results suggest that the problem can be avoided by optimizing the mold flow pattern and powder properties to obtain adequate liquid flux coverage and uniform shell growth; and by optimizing mold taper, water sprays, roll alignment and decreased roll spacing.
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