Effect of Manganese on the Formation Mechanism of Nonmetallic Inclusions in Fe-xMn-7Al-0.7C Lightweight Steel

Herein, the effect of Mn content on the formation of noninclusions in lightweight steels is investigated. In addition, the precipitation behavior of MnS inclusions during solidification under different manganese contents (3%, 10%, 20%, and 30%) is analyzed with help of a microsegregation model. The results show that the inclusions formed are classified into seven types: Al2O3, Al2O3-MnS, AlN, MnS, AlN-MnS, Al2O3-AlN, and Al2O3-AlN(AlON)-MnS in the steel. As the Mn content increases from 3% to 30%, the total area ratio and total number density of inclusions increase, especially AlN-containing inclusions and MnS-containing inclusions. The thermodynamic results of inclusion types calculated with FactSage are consistent with the observed results. When the Mn content ranges from 3% to 30%, both Al2O3 and AlN inclusions can exist stably at the steelmaking temperature, and MnS inclusions can precipitate in the mushy zone alone. With the enhancement of Mn content, the precipitation temperature of MnS inclusions decreases, and the solid fraction decreases during solidification. Moreover, it is found that Mn content can significantly affect the morphology of the precipitated MnS, and an increase in Mn content can promote the divorced eutectic transformation of MnS to form polyhedral MnS.