Mitigation of Edge Cracks by Controlling the Manganese-to-Sulfur Ratio (Mn/S) in Low Carbon Boron Steel

The formation of edge or surface cracks on continuous cast slabs is a significant problem as these increase the slab processing cost and affect the quality of hot/cold rolled coils. The edge crack formation is greatly influenced by slab composition, caster operation and machine maintenance strategies. The manganese-to-sulfur (Mn/S) ratio of low carbon steels has a significant effect on the formation of edge cracks. The effect of Mn/S ratio on hot ductility and edge crack tendency was investigated for low carbon boron steel over a temperature of 600–1100 °C using a Gleeble thermomechanical simulator. The temperature range of low ductility is a strong function of the Mn/S ratio, and this range decreases with an increase in Mn/S ratio. The underlying mechanism for low ductility is discussed using fractographs and microstructure. Edge cracks on slabs of this grade can be eliminated by maintaining the Mn/S ratio greater than 36 to narrow the low ductility temperature range and ensuring the surface and corner temperature of the slab beyond the temperature range of low ductility especially during unbending. A hard or soft secondary cooling strategy is recommended to maintain the surface and corner temperature of slabs beyond the low ductility temperature range.