2017 Volume 57 Issue 9 Pages 1537-1545
Industrial and laboratory experiments were carried out to understand the formation and evolution mechanism of non-metallic inclusions in medium Mn steel during secondary steelmaking process. In industrial experiments, with the generation of dissolved Mg and Ca in liquid steel, the inclusions in liquid steel would transform along with the route of “Al2O3 inclusions → MgO·Al2O3 spinel inclusions → (Mn, Mg)O·Al2O3 spinel inclusions → CaO–MgO–MnO–Al2O3 system calcium aluminate inclusions”. (Mn, Mg)O·Al2O3 spinel with a high MnO content was found as a different type of inclusions compared with conventional Al-killed steel grades, and finally, the MnO content in calcium aluminate inclusions became very low. Laboratory experiments were employed to explain the generation of (Mn, Mg)O·Al2O3 spinel inclusions. It is found that the crystal structure of MgO·Al2O3 spinel phase would help the formation of (Mn, Mg)O·Al2O3 spinel inclusions, while Al2O3 inclusions can not react with dissolved Mn in steel to form (Mn, Mg)O·Al2O3 spinel inclusions, even the Mn content was around 5 mass% in steel. Consequently, (Mn, Mg)O·Al2O3 spinel inclusions formed after the formation of MgO·Al2O3 spinel inclusions in industrial practice.
