Formation Mechanism of AlN-MnS Complex Inclusions in Fe-5Mn-2Al-0.15C Medium Mn Steel

The formation mechanism of AlN-MnS complex inclusions in Fe-5Mn-2Al-0.15C medium Mn steel was investigated under as-cast conditions by microstructure observation, thermodynamic analyses, and the Clyne-Kurz microsegregation model. The results showed the variations in the maximum and minimum partition coefficients for N and S were relatively large, and that the maximum diffusion coefficients of solute N, S, Mn and Al were more than 70% more than the minimum ones. Therefore, the variable partition coefficients and variable diffusion coefficients of solute elements under different temperatures should be considered in the Clyne-Kurz model during the solidification process. The partition coefficients of Al were higher than 1, segregating into the dendrite interior. However, the partition coefficients for elements N, Mn, and S were lower than 1, enriching in the residual liquid steel. By the Clyne-Kurz model considering the variable partition coefficients and variable diffusion coefficients, the precipitation temperatures of AlN and MnS were 1738 K and 1717 K during the solidification process, respectively. With experimental observation, the formation of AlN-MnS complex inclusions during the solidification process may be the AlN acting as a nucleation site for MnS, and then MnS wrapped or attached to the surface of AlN.

Automated summary

The formation mechanism of AlN-MnS complex inclusions in Fe-5Mn-2Al-0.15C medium Mn steel under as-cast conditions was investigated through microstructure observation, thermodynamic analyses, and the Clyne-Kurz microsegregation model. The results showed that the variations in partition coefficients and diffusion coefficients of solute elements should be considered in the Clyne-Kurz model during the solidification process. The precipitation temperatures of AlN and MnS were determined as 1738 K and 1717 K, respectively, by the Clyne-Kurz model considering variable partition coefficients and diffusion coefficients.