Evolution Mechanism of Inclusions in Medium-Manganese Steel by Mg Treatment with Different Aluminum Contents

To investigate the effect of magnesium addition on the evolution of inclusions in medium-manganese steel with different aluminum contents, both thermodynamic calculation and high-temperature simulation experiments were carried out in the present work. The in situ observation experiments were used to clarify the related evolution process of inclusions. The samples taken from the melts were analyzed by scanning electron microscopy and energy dispersive spectroscopy. The compositions of steel were determined by inductively coupled plasma-optical emission spectrometer. The results show that the aluminum content in steel has a certain influence on the magnesium content, under the same conditions, magnesium content increases with increasing aluminum content. The inclusions transformed from MnO·Al₂O₃ to Al₂O₃ when the aluminum content was higher than 0.0076 mass pct. After magnesium treatment, the inclusions gradually transformed into MgO·Al₂O₃, and the MgO/Al₂O₃ mole ratio in inclusions decreased with the increase of aluminum content. The diameter of the inclusions decreased, and number density of inclusions increased in steel after magnesium addition. The phenomenon that large-sized cluster-like Al₂O₃ inclusions transform into finely dispersed Mg-containing inclusions was firstly observed in situ by confocal laser scanning microscope.