Formation and Control of Transverse Corner Cracks in the Continuous Casting Slab of a Microalloyed Steel

To investigate transverse corner cracks for a microalloyed steel continuous casting slab, the metallography, microtopography, and three-dimensional (3D) morphology of cracks are studied, respectively. High-temperature mechanical properties are investigated and compared from two positions where samples are extracted from both the slab corner and surface of the slab center. The thermal history of the slab is simulated and optimized experiments are conducted. Transverse corner cracks are generated on the valley of oscillation marks. Mold powder and wear elements of the mold are not detected. Microstructures are refined near the cracks. Cracks are generated in secondary cooling zones and the cracking temperature is higher than Ar-3 temperature. The extension path of cracks is not linear and cracks extend along the grain boundary. The third brittle temperature ranges (TBTR) are 764-832 degrees C and 793-808 degrees C in the two positions, respectively. The temperature at the slab corner in the bending and straightening zone falls into the brittle zone during the original water cooling condition, leading to the formation of cracks. The secondary cooling scheme is optimized to prevent the temperature at the slab corner in the bending and straightening zone from entering the TBTR, significantly reducing the occurrence of transverse corner cracks.