Refinement mechanism of cerium addition on solidification structure and sigma phase of super austenitic stainless steel S32654

The influence of Ce addition on the solidification structure and sigma phase of super austenitic stainless steel S32654 was systematically investigated via microstructural characterization and thermodynamic calculation. The results indicate that a small addition of Ce could modify MgO and MnS into Ce-bearing inclusions Ce2O3 and Ce2O2S. Ce addition led to noticeable refinement of both the dendrite structure and sigma phase. The refinement mechanism could be attributed to the combined actions of effective Ce-bearing inclusions and solute Ce. Effective Ce-bearing inclusions could serve as heterogeneous nucleation cores of austenite as well as sigma phase, which provided a favorable prerequisite for their refinement. Solute Ce significantly enhanced the undercooling degree of the system, further promoting dendrite structure refinement. Meanwhile, solute Ce improved the eutectic precipitation conditions of sigma phase and further promoted its nucleation, while the dendrite refinement limited its growth space. Finally, more fine and dispersed sigma phase particles formed in 532654 with Ce addition. The refinement of dendrite structure and sigma phase will reduce the temperature and time required for high-temperature homogenization, which is beneficial to the hot working of this steel. (C) 2022 Published by Elsevier Ltd on behalf of The editorial office of Journal of Materials Science & Technology.