Evaluation of longitudinal cracks in thin slab using coupled fluid flow and thermo-mechanical numerical modelling approach

Longitudinal facial cracks (LFC) are one of the major surface defects in thin slab casting (TSC) that adversely impact the quality and integrity of the cast slab. These defects are primarily due to the complex nature of coupled thermo-mechanical phenomena during TSC through funnel mould. The unique shape of funnel mould results in shell deformation during solidification, leading to hot tearing and crack propagation. In the present work, a coupled thermo-fluidic-mechanical model is developed to predict fluid flow, solidification and stresses in the solidifying shell in an industrial thin slab caster mould. The finite element method (FEM)-based mathematical model is coupled with computational fluid dynamics (CFD) solver to predict the solidified shell thickness, three-dimensional temperature fields and corresponding stresses. Analysis of stress state during solidification indicates region of high stress along the funnel edges. Such stresses coupled with the weak solidified shell may result in defects during casting. In TSC operations, LFC is observed to vary in length depending on severity and may range from few centimetres to metres in adverse cases. These cracks are about 1 mm to 2 mm in depth and tend to form 0.1 m to 0.4 m below the meniscus. Such defects lead to about 15% downgrading at the TSC.