Effect of Rare-Earth La on Inclusion Evolution in High-Al Steel

作者：Li, Bin; Zhu, Hangyu^*; Zhao, Jixuan; Song, Mingming; Li, Jianli^*; Xue, Zhengliang

来源：Steel Research International, 2022, 93(2): 2100347.

DOI：10.1002/srin.202100347

• Al2O3 inclusion
• AlN inclusion
• high-Al steels
• inclusion modification
• La addition
• nonmetallic inclusions

To investigate the evolution of inclusions in high-Al steel with addition of La, a series of laboratory experiments and thermodynamic calculations are performed, considering the reaction time and amount of La added. The main inclusions in the high-Al steel without the addition of La are Al2O3, MnS, and Al2O3-MnS. The La treatment can efficiently modify Al2O3 to La-Al-O or La-O-S inclusions. For La additions less than 0.0041 wt%, the evolution route for the inclusion in high-Al steel is Al2O3 -> LaAl11O18 -> LaAlO3 with an increase in reaction time. For high La additions, the evolution route for the Al2O3 inclusion is Al2O3 -> LaAl11O18 -> LaAlO3 -> La2O2S -> La2S3. The experimental results correlate with those of the thermodynamic analysis. Notably, excess La in high-Al molten steel may consume O and S to form La oxysulfide and sulfide, respectively, which prevents the precipitation of MnS inclusion and promotes the formation of AlN inclusion during solidification.