Evolution of Inclusions in Incoloy825 during Electroslag Remelting

Fifty kilogram-scale electroslag remelting (ESR) experiments using slag with different TiO2 contents in an electroslag furnace were performed to investigate the size, amount and types of inclusions in an electrode and remelted ingots. The results show that the contents of aluminum and titanium increased and decreased, respectively, compared to those in a consumable electrode. The inclusions in the consumable electrode were TiS, TiN and Al2O3 surrounded by a TiN layer, and the inclusions in the remelted ingots were TiN, MgO-Al2O3 and MgO-Al2O3 surrounded by a TiN layer. With the increase in the height of the ingots, the average size of inclusions increased from 2.5 to 4.4 μm. Increasing the TiO2 content in the slag promoted the formation of MgO-Al2O3 and made the inclusions larger in the remelted ingots. To make the size of inclusions in remelted ingots of Incoloy825 smaller, the TiO2 in the slag should be decreased. The TiS in the electrode was removed during ESR. Part of the TiN dissociated during the reaction between the liquid metal and slag by molten slag, and most of the TiN inclusions originated from the consumable electrode. The Al2O3 inclusions surrounded by a TiN layer in the consumable electrode were finally transformed to MgO-Al2O3 and MgO-Al2O3 surrounded by a TiN layer in the remelted ingots.