The target of this research was to identify the occurrence of the longitudinal facial crack (LFC) defect during the casting of a low-carbon, low-manganese flat steel product. Despite the severity of this defect which may be minor, it turned out unacceptable in the final product due to the remarkable production losses associated with reproducing the product. Electrochemical testing was executed on samples of the LFC defect, which were compared to a control sample. Additionally, Selected LFC samples were also analyzed using scanning electron microscopy and energy-dispersive X-ray spectroscopy at various process parameters such as carbon equivalent, isostatic flow control, non-metallic inclusion, mold flux to determine the root cause of the LFC defect. The findings of this investigation revealed that optimizing specific process parameters in both the thin slab caster and the melt shop effectively controlled the appearance of LFC defects. By manipulating these parameters, it was possible to mitigate the occurrence of LFC defects and prevent the associated economic losses, which result from having to reproduce the product. The likelihood of LFC defects can be drastically reduced by identifying and solving the underlying root causes of the defect, such as adjusting carbon equivalent, isostatic flow control material, managing non-metallic inclusions, and improving mold flux. These results underline how crucial it is to properly optimize the process variables in order to guarantee the manufacture of premium low-carbon, low-manganese flat steel products.