Effects of Titanium Oxide Precipitates on the Acicular Ferrite Nucleation in Carbon Structural Steel

The features of inclusions and microstructure for Ti-added carbon structural steel (C: 0.26 wt.-%) were studied by scanning electron microscope (SEM) and energy dispersive spectrometer (EDS). After etching, it has been found that the titanium oxide can act as nucleation site for acicular ferrite. Moreover, from the SEM-EDS mapping images, it can be seen that the MnO-SiO2 phase occupies the core of nucleation inclusion, and the titanium oxide precipitates on them. This result can be explained by theoretical calculation, and this kind of precipitation does not lead to inclusion coarsening. Furthermore, the element sulfur accumulates on the periphery of nucleation oxides, which implies the absorption of MnS plays an important role for the acicular ferrite formation. These results confirm that titanium oxide precipitate can also induce the acicular ferrite formation, and may gain new insights in the oxide metallurgy.