Effects of Ti and Al addition on the Formation and Evolution of Inclusions in Fe-17Cr-9Ni Austenite Stainless Steel

The effect of titanium and aluminum contents on the formation and evolution of inclusions were investigated in Fe-17Cr-9Ni austenite stainless steel at 1873 K. Homogeneous spherical FeO_y-CrO_z-MnO-SiO₂ was the main inclusion before titanium and aluminum were added. Thermodynamic calculations indicated that when the Al content exceeds 0.0085 wt pct and Ti content exceeds 0.036 wt pct, spherical FeO_y-CrO_z-MnO-SiO₂ inclusions can be reduced to irregularly shaped Al₂O₃ and TiO_x inclusions, respectively. The formation of TiN on the surface of Al-Ti-O inclusions can prevent the reduction of Al-Ti-O by Al or Ti. Moreover, the different formation mechanisms of Al-Ti-O inclusions and TiN are discussed. When Ti was added to reduce Al₂O₃, the added Ti initially caused the formation of Al-Ti-O inclusions and then reacted with N in the molten steel to form TiN. On the other hand, in the case of the addition of Al to reduce TiO_x, the formed reduction products were Al-Ti-O inclusions and Ti dissolved in molten steel, the latter being an important source of Ti in the later formed TiN. The TiN found in the experimental samples is more likely to be formed in molten steel at a temperature of 1873 K than during cooling.