Effect of aluminum on the nucleation of intragranular ferrite in Ti-added carbon structural steel

The features of inclusion and microstructure for Ti-added carbon structural steel were studied through the scanning electron microscope (SEM) and Energy Dispersive Spectrometer (EDS). From the SEM-EDS mapping images, two kinds of titanium-contained oxides are observed. The type I is the Al-Ti-O phase, in which the elements of Al and Ti coexist. The type II is the titanium-contained oxides, which precipitate on the Al2O3. Through the statistical analysis, it can be seen that the former type is dominating in number and smaller in size. After etching, the microstructure of intragranular acicular ferrites (IAF) is observed, which is totally different from that in the comparison sample without Ti addition. Furthermore, it's found that the type I inclusion can act as nucleation sites for the IAF. However, the similar nucleation phenomenon is complex for the type II inclusion. This complexity is attributed to the diversity of precipitation of Ti and Mn.