Thermodynamic study of Ti₂O₃+TiN complex nucleus formation in 430 ferritic stainless steel

The principles of Ti₂O₃ and TiN formation in 430 ferritic stainless steel were theoretically analyzed. The steel's compositions including Ti, Al, O and N for forming Ti₂O₃ + TiN complex nuclei on solidification fronts were put forward. According to composition requirements, the experiment was conducted in a vacuum induction furnace to get an ingot. Some metallographie samples were prepared for observing the feature of precipitates under scanning electron microscopy (SEM) and transmission electron microscope (TEM). It was observed by SEM that these precipitates were fine and dispersively distributed. Their sizes were about 2 μm and titanium nitride precipitates around titanium oxide. It was further confirmed by TEM diffraction patterns of precipitates that the center layer of precipitates was Ti₂O₃ and the outer layer of precipitates was TiN. If the steel's composition was reasonably controlled, Ti₂O₃ + TiN complex nuclei can form even under a low titanium content.