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

Abstract

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, TixOy, MnS, Al2O3, and MgAl2O4. Thermodynamic calculation results suggest that the transformation order of Al2O3 contains two pathways: one is Al2O3 → MgAl2O4 → MgTi2O4 → MgO and the second is Al2O3 → Ti2O3 → MgTi2O4. However, the transformation reaction of Al2O3 into MgAl2O4 or Ti2O3 has not completely ended, and no MgTi2O4 and MgO inclusions are found in the steel sample. The precipitation order of Ti2O3, TiN, TiS, and MnS in present steel is Ti2O3 → 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 Al2O3 → MgAl2O4 → Ti2O3 → TiN → TiS → MnS or Al2O3 → Ti2O3 → TiN → TiS → MnS.