Evolution of Desulfurization and Characterization of Inclusions in Dual Alloy Ingot Processed by Electroslag Remelting

Desulfurization and characterization of inclusions during ESR of dual alloy ingot were experimentally studied. The composition and inclusions in electrode and ESR ingot were analyzed by means of various analytical techniques. The results show that the size of inclusions in ingot is smaller and more uniform. The single larger (Mn,Cr)S inclusion (11.6 mu m) is found in NiCrMoV electrode. But, no single (Mn,Cr)S inclusion is found in NiCrMoV and CrMoV zones in dual alloy ingot, whereas found in transition zone (TZ). The size of inclusions in TZ is larger than that in NiCrMoV and CrMoV zones due to the inclusions with a thicker (Mn,Cr)S layer and large (Mn,Cr)S inclusions in TZ. Thermodynamic calculations show that (Mn,Cr)S inclusions with high x(Mn)/x(Cr) can precipitate at the solidification front of TZ due to the enrichment of [Mn] and [S] in residual liquid steel. To eliminate (Mn,Cr)S inclusions, a deeper desulfurization is needed. The sulfur content decreases from 0.039 (mass pct) to 0.0171% in NiCrMoV zone and from 0.011 to 0.0017% in CrMoV zone. The gasifying desulfurization plays a dominate role, the ratio of gasifying desulfurization is 92.2%.