Herein, the effect of Mn content on the characteristics and the formation of inclusions in light‐weight Fe–Mn–Al steels is investigated. Three laboratory‐produced steels, containing different manganese contents (2%, 5%, and 20%) are investigated. 2D and 3D inclusion characterization methods are used to establish inclusion classification rules for oxide, sulfide, and nitride inclusions using an automated scanning electron microscope (SEM) equipped with energy‐dispersive X‐ray spectroscopy (EDS) (ASPEX system). The observed inclusions are classified into Al2O3(pure), Al2O3–MnS, AlN(pure), AlN–MnS, AlON–MnS, AlON, and MnS. The results show that an increased Mn content of steel increases the number of inclusions, especially Al2O3–MnS and AlN–MnS inclusions. In the case of Al2O3–MnS inclusions, Al2O3 inclusions serve as the site for precipitation of MnS. Thermodynamic calculations suggest that the AlN‐containing inclusions formed during cooling and solidification of steels. Moreover, the formation of AlN–MnS inclusions can take place by the nucleation of MnS on AlN inclusions and vice versa.

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The effect of Al content on the characteristics and formation of inclusions in the light-weight Fe-5Mn-xAl steels was investigated in this study. Four synthetic steels with different Al content were produced in the laboratory. The types of observed inclusions were Al 2 O 3(pure) , Al 2 O 3 -MnS, AlN (pure) , AlN-MnS, AlON-MnS, AlON and MnS. Increasing Al content from 0.5% to 6% increased the total amount of inclusions by 2.5 times. As the Al content increased from 0.5% to 3%, the number of AlN-MnS inclusions increased significantly. Moreover, the AlN(pure) inclusions appeared in 6% Al containing steel. Thermodynamic calculations confirmed that AlN inclusions formed during cooling of the steel. It is also observed that AlN can precipitate on Al 2 O 3 to form AlN + Al 2 O 3 inclusions, classified as multi-phase AlON inclusions in this study. Furthermore, MnS inclusions could co-precipitate with AlN and Al 2 O 3 inclusions, but it preferred to co-precipitate with AlN inclusions.

This study focused on the characteristics of complex MnS inclusions in advanced high strength steels. The effect of metal chemistry (Al and N) and the cooling rate of steel were evaluated by analyzing the inclusions present in five laboratory produced steels. The observed complex MnS inclusions contained Al2O3-MnS, AlN-MnS, and AlON-MnS. An increase in Al content from 0.5% to 6% increased the number of complex MnS inclusions by ~4 times. In comparison, a decrease of ~80% was observed due to the increased N content of steel from <10 ppm to ~50 ppm. MnS precipitation ratio was used to determine the potency of different inclusions forming complex MnS inclusions due to heterogeneous nucleation. It was found that the MnS precipitation ratio of the observed inclusions was related to their misfit with MnS, and it decreased in the order of AlN > AlON > Al2O3. Moreover, it was determined that AlN particles could be easily engulfed at the solidification front relative to Al2O3, which resulted in a higher MnS precipitation ratio for Al2O3 under slow cooling conditions.

The effect of N content on the characteristics and formation of inclusions in the Fe-5Mn-3Al steels was investigated in this study. Two synthetic steel melts were produced by two different methods—N2 gas purging and injecting—to introduce nitrogen into the melt. The N content of steel melt varied from 2 to 54 ppm. An increase in the N content to 47 ppm (for 533N-P) and 58 ppm (for 533N-I) increased the total amount of inclusions from 13 to 64 mm−2 and from 21 to 101 mm−2, respectively. The observed inclusions were Al2O3(pure), Al2O3-MnS, AlN(pure), AlN-MnS, AlON, AlON-MnS, and MnS. When the N content was less than 10 ppm, AlN-MnS inclusions were the primary type of inclusions and they formed as solidification products. With an increase in the N content, AlN(pure) inclusions became the dominant type of inclusions as AlN was stable in the liquid steel. These findings were confirmed by thermodynamic calculations. The influence of cooling rate on the types of inclusions was studied and a higher number of AlN-MnS inclusions were observed in samples with slow cooling rate.