LAUSR

The deterioration of impact toughness in central segregation zones poses a critical challenge for microalloyed steel ultra‐thick slabs. The distribution of (Ti, Nb, V) N precipitates and its correlation with impact toughness in microalloyed steel ultra‐thick slabs are investigated in this study. Results show that the proportion of (Ti, Nb, V) N precipitates larger than 5 μm in the central region reaches 34.2%, significantly higher than that in the surface with a value of 9.1%, due to the lower cooling rate and severe central microsegregation. The WIRS‐VB microsegregation model calculated that TiN begins to precipitate at a solid fraction of 0.39, which is much earlier than the surface region with a solid fraction of 0.76. The large‐sized (Ti, Nb, V) N precipitates of ≈12 μm appear on the secondary crack of the fracture morphology in the central region, which act as initial sites for crack initiation, ultimately reducing the impact toughness of 20.5%.