Inclusion degeneration and resultant coarsening in a Ce-treated 9% Cr heat-resistant steel during electroslag remelting

The evolution of inclusions in a 12-ton Ce-treated 9%Cr martensitic heat-resistant steel during vacuum induction melting and electroslag remelting was investigated. The addition of Ce in VIM converted Al 2 O 3 and Al 2 O 3 ·SiO 2 inclusions into finer Ce 2 O 3 and Ce 2 O 2 S, reducing the average inclusion size from 2.29 μm to 2.01 μm. However, the reaction between dissolved Ce and slag Al 2 O 3 during ESR caused a significant decrease in Ce content and degenerated the inclusions into CeAlO 3 , leading to the coarsening of inclusions. Thermodynamic calculations using the Ion-Molecule Coexistence Theory showed that reducing Al 2 O 3 content in slag while increasing Ce 2 O 3 content can partially suppress the reaction between Ce and Al 2 O 3 , thereby mitigating Ce oxidation during ESR. Based on FactSage simulations, maintaining Ce content between 0.005 and 0.02 wt% in the ESR ingot is essential to avoid the formation of harmful inclusions such as CeAlO 3 and Al 2 O 3 .