Cerium (Ce) was effectively transitioned into the high-Mn austenitic steel weld metal under submerged arc welding by adding cerium dioxide and calcium silicon reducing agents into flux. The evolution behaviours of the composition, number density and size of inclusions in weld metal with different Ce contents were systematically investigated by thermodynamic calculation and experiments. The results show that the number density of inclusions increased and average size decreased with the increase of Ce content from 0 to 0.087 wt-%. Meanwhile, and the percentage of inclusions number with size less than 0.80 μm increased from 79.28% to 91.43%. The evolutionary process of inclusions was Al2O3 → Al11O18Ce → CeAlO3 → Ce2O3 → Ce2O2S with the increase of Ce content in the present weld metal. In particular, Ce-O-S-Al inclusion was extracted by in-situ sample preparation method, which proved its internal structure and evolution process. The complete formation model of Ce-Al-O-S system was also established.
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