The roles of Ce and Mn on solidification behaviors and mechanical properties of 7Mo super austenitic stainless steel

Effect of Ce and Mn on solidification behaviors and mechanical properties of 7Mo super austenitic stainless steel was investigated via in-situ observations, thermodynamic calculations and microstructural characterization. The results show that the network eutectic microstructure had higher hardness compare with ordinary cast structure. And increasing Ce and Mn can both improve the hardness which could be attributed to the effect of Ce and Mn on the solidification microstructure. Analyses indicate that Ce acted as inclusions and atoms to shorten the solidification interval and refine the microstructure to reduce the σ phase. This finer microstructure increased the average hardness. While increasing Mn content modified Ce–O inclusions into Ce–Mn–O compound inclusions which reduced nucleation sites. Mn also promoted the segregation of Cr and Mo in the liquid to decrease the solidification rate, leading to microstructure coarsening and high content of σ phase. This study may provide a theoretical basis for the composition design and applications of the 7Mo super austenitic stainless steel.