Evolution of Al–Ti Oxide Inclusions in Fe-Based Alloys During Thermal Holding by a Novel Inductive Separation Method

Steelmaking has undergone significant technological advancements, particularly regarding oxide metallurgy. Herein, we employed a novel method of inductive separation for separating Al–Ti oxide from Ti-bearing oxides to trace the evolution of a specific type of oxide in a solid Fe-based alloy during thermal holding. The evolution occurred within the solid alloy; hence surface effects were prevented. The evolution was investigated at a lower temperature than what was used in previous studies; using this information, the impact of temperature was ascertained. The results revealed that, after holding for 0.5 hours at 1273 K, the shape of the Al–Ti oxide changed from spherical to irregular. The homogeneous oxide changed to a heterogeneous oxide containing Al- and Ti-rich parts, and the compositional deviation became distinct after thermal holding. After 12 hours, the composition of the Al-rich parts approached that of Al₂O₃. A comparison of the variation of the Al–Ti oxide at 1273 K and 1573 K revealed that the ratio of the heterogeneous oxide increased at lower temperatures due to the greater degree of supersaturation of Al₂O₃. The mechanism involved the precipitation of Al₂O₃ from Al–Ti oxide during holding. The fundamental data on the time-dependent variation in the morphology and composition of the Al–Ti oxide function as a first step to modify the oxide using thermal holding to promote the induction of an intragranular acicular ferrite (IAF) microstructure.