Effects of Atmosphere and Na₂O in Slag on Inclusion Characteristics of Al-Killed Fe–18Cr–18Mn Remelted by (P)ESR Process

The evolution of inclusions in pressurized electroslag remelting (PESR) ingots and the effects of atmosphere and Na₂O in slag on inclusion characteristics were studied by experiments and thermodynamic analyses. The inclusions in the electrode were numerous MnS and complex oxides with MnS layer. The MgO·Al₂O₃ and Al₂O₃ oxides formed first in liquid steel during cooling, and subsequently MnS precipitated independently or with oxides as core in virtue of micro-segregation. The (P)ESR process exerted remarkable desulfurization and inclusion removal, while the average size of inclusions increased due to elimination of small-size MnS. During remelting, the original sulfides were dissociated as dissolved sulfur and were mostly removed, but then a few sulfides re-formed during solidification. The Al₂O₃ and MgO·Al₂O₃ were difficult to be completely dissolved, and were partially absorbed by slag. Compared with air atmosphere, the quantity of sulfur-containing inclusions in ingots remelted under pressurized nitrogen significantly increased because of the weakened gasifying desulfurization, while the effect of pressure was negligible. Na₂O addition in slags reduced the sulfide inclusions in ingots by enhancing desulfurization ability. It also decreased the area ratio and size of inclusions by promoting the adsorption of original large-size inclusions. However, 8 wt pct Na₂O addition caused the slight increases in oxygen content and inclusion quantity due to Na₂O decomposition.