Effect of Rare‐Earth Cerium on Nonmetallic Inclusions in Novel Cryogenic High‐Mn Steel

This work focuses on the key issue of inclusions that results from the failure of novel cryogenic high‐Mn steel, and the rare‐earth Ce modification of inclusions were investigated by laboratory experiments and thermodynamic calculations. The effect of Ce content on the evolution behavior of inclusions was discussed. The results show that the inclusions in the cryogenic high‐Mn steel after adding Ce transformed from pointed corners and irregular‐shaped Al 2 O 3 –MnS, MnS–AlN, and MnS–Al 2 O 3 –AlN into AlN–Ce 2 O 3 , AlN–Ce 2 S 3 , AlN–Ce 2 O 3 –Ce 2 S 3 , CeAlO 3 –Ce 2 S 3 –AlN, and single Ce 2 S 3 . Besides, the higher the Ce content is, the easier the transformation into Ce 2 S 3 is. Furthermore, the thermodynamic calculations indicate that the MnS and AlCeO 3 can be converted to Ce 2 S 3 during solidification, and precipitation order of inclusions containing Ce steel is as follows: AlCeO 3 → MnS → AlN → Ce 2 S 3 . In contrast, when Ce content is further increased to 33 ppm, Ce 2 S 3 and MnS were precipitated simultaneously, and trace amounts of AlCeO 3 inclusions remain. Moreover, the Ce‐modification mechanism of inclusions in cryogenic high‐Mn steel mainly includes two substitution reactions: One, reaction of Al in the original Al 2 O 3 was replaced by Ce to form AlCeO 3 occurred in molten steel, and the another one is that Mn in MnS was replaced by Ce to form Ce 2 S 3 occurred at the end of solidification.