Precipitation Behavior of TiN and Its Influence on Microstructure and Hardness in Ti‐Microalloyed Steel Slabs

This study systematically investigates the precipitation behavior of TiN and its influence on microstructure and hardness in titanium‐microalloyed steel slabs. Two low‐carbon microalloyed steel slabs with different Ti contents (0.0665 and 0.0766 wt%) were prepared, and samples were taken from the surface, 1/4 thickness, and 1/2 thickness positions. The microstructure, TiN characteristics, and texture were analyzed by optical microscopy, scanning electron microscopy, and X‐ray diffraction. Vickers hardness was measured, and a hardness prediction model was established based on ferrite fraction, pearlite fraction, TiN area fraction, and grain size. Combined with thermodynamic (lever rule and V–B microsegregation model) and kinetic growth models, the precipitation mechanism during solidification was revealed. The results show that the experimental steels primarily consist of ferrite and pearlite, with main textures of {110}<110> and {110}<001>. The established hardness model exhibits a high fitting accuracy ( R ²  = 0.94) and holds certain reference value. TiN particles are predominantly enriched at the 1/4 thickness position with the largest size, exhibiting various morphologies, including irregular, square, rectangular, hexagonal, and octahedral shapes. They also form composite inclusions with MnS, MgO, and MgAl ₂ O ₄ , following a precipitation sequence of Al ₂ O ₃  → MgAl ₂ O ₄  → MgO → TiN → MnS. Thermodynamic analysis indicates that TiN cannot precipitate in the liquid phase but can form in the solid–liquid two‐phase region induced by solute segregation. During solidification, Ti concentration increases monotonically, while N concentration first increases and then decreases; the TiN radius increases sharply when the solid fraction reaches approximately 0.9. Furthermore, TiN may act as a heterogeneous nucleation site for pearlite, and various cementite morphologies are observed.