Competition and Precipitation Mechanism of Inclusions in the Al–Ti–Mg Complex Deoxidized Steel

In this work, the competitive precipitation mechanism of inclusions in Al–Ti–Mg complex deoxidized steel is investigated by experimental observation and thermodynamic analysis. Many types of inclusions are observed in steel, and the two and multi‐layer structural inclusions are composed of the single‐particle inclusions of TiS, TiN, Ti x O y , MnS, Al 2 O 3 , and MgAl 2 O 4 . Thermodynamic calculation results suggest that the transformation order of Al 2 O 3 contains two pathways: one is Al 2 O 3 → MgAl 2 O 4 → MgTi 2 O 4 → MgO and the second is Al 2 O 3 → Ti 2 O 3 → MgTi 2 O 4 . However, the transformation reaction of Al 2 O 3 into MgAl 2 O 4 or Ti 2 O 3 has not completely ended, and no MgTi 2 O 4 and MgO inclusions are found in the steel sample. The precipitation order of Ti 2 O 3 , TiN, TiS, and MnS in present steel is Ti 2 O 3 → TiS → TiN → MnS. MnS only precipitated in solid steel, TiS, and TiN precipitated in the solid–liquid interface at T < 1794 K and T < 1796.5 K, respectively. The actual transformation and precipitation order of inclusion in the present Al followed by Ti–Mg deoxidized steel is Al 2 O 3 → MgAl 2 O 4 → Ti 2 O 3 → TiN → TiS → MnS or Al 2 O 3 → Ti 2 O 3 → TiN → TiS → MnS.