Study on Transverse Surface Cracks in the Continuous Casting Slab of a Microalloyed Steel

Transverse surface cracks are one of the main surface defects which limit the quality and efficiency of microalloyed steel production. Herein, controlling strategy of transverse surface cracks is investigated. Transverse surface cracks are often formed in the valley of oscillation marks on the loose side surface in the continuous casting slab. The cracks are investigated using an optical microscope and scanning electron microscope. Then the hot ductility is measured, and the thermodynamics of precipitates are calculated. Finally, the temperature history of the slab is calculated, and the secondary cooling water flow rate is optimized. Mold powder and wear elements of the mold are not detected. The ferrite is almost symmetrically distributed on both sides of the crack. Transverse surface cracks are generated in the secondary cooling zones. In the straightening zones, the temperature on the loose side of the continuous casting slab near the quarter of the edge falls in the third brittle temperature range which is the reason for the generation of transverse surface cracks. The content of N in the steel is controlled below 0.003%, and the water flow in the secondary cooling zones from zone 5 to zone 8 is increased by 60%. Transverse surface cracks disappear.