Microstructure, inclusions and cryogenic impact toughness of Fe-22.03Mn-0.45C austenitic weld metal were investigated. The results show that microstructure of weld metal consisted of straight columnar dendrites with different orientations. Microsegregation of Mn was observed in the interdendritic regions and Mn depletion thus occurred in the dendrite core, which is suggested to lead to the different morphologies of MnS oxides (Mn–Al–Si–O) depending on their location. MnS patch-type oxides were found at dendrite boundary and MnS shell-type oxides were found at dendrite core. Inclusions as crack sources were distributed in the dimple of cryogenic impact fractography, it was found that MnS patch-type oxides were more ready to act as a crack source and cause the formation of dimples than MnS shell-type oxides.
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