Yttrium-Induced Modulation of Solute Partition and σ-Phase Suppression in the Solidification of 7Mo Super-Austenitic Stainless Steel

The effect of yttrium on solute redistribution and σ-phase precipitation in high-Mn and high-Mo super-austenitic stainless steel during solidification is studied by directional solidification experiments and thermodynamic calculations. Investigate the interactions between yttrium and other major alloying elements (such as Mn and Mo) and their effects on the solidification process. Thermodynamic calculations indicate that yttrium enriches in the residual liquid phase and promotes the segregation of Mn toward the liquid phase while inhibiting the segregation of Mo toward the liquid phase. Combining with the electron backscatter diffraction results of directionally solidified samples, it is shown that the σ phase decreased by ≈30%. η_i,j is the interaction parameter between solutes. After the addition of yttrium, η_Mo,_Mn increases significantly from −0.02571 to −0.0027; η_Mo,Mo increases from −0.00345 to −0.0029. In other words, yttrium promotes the enrichment of Mn into a liquid phase and inhibites the enrichment of Mo.