Evolution and Formation of Non-Metallic Inclusions during Electroslag Remelting of Ce-Bearing 15Cr-22Ni-1Nb Austenitic Heat-Resistant Steel

Abstract

The evolution of inclusions in austenitic heat-resistant steel with different Ce content during protective argon gas atmosphere electroslag remelting (ESR) was studied. All oxide inclusions in the Ce-free consumable electrode are MgO·Al2O3. A part of these MgO·Al2O3 inclusions was removed before metal droplets entered the liquid metal pool during the ESR. The soluble oxygen (arising from the reoxidation) reacted with soluble aluminum, calcium, and magnesium in liquid steel to form MgO·Al2O3 and CaO–Al2O3 inclusions in liquid steel. All oxide inclusions in the electrode with 0.016 mass% Ce are Ce2O2S. A portion of these Ce2O2S inclusions was dissociated into soluble oxygen, cerium, and sulfur in liquid steel during the ESR process, whereas the others were removed by absorbing them into molten slag. The oxide inclusions in the liquid metal pool and remelted ingot were Ce2O3, CeAlO3, and Ce2O2S. The CeAlO3 and Ce2O3 inclusions were reoxidation products formed by the chemical reaction between the soluble oxygen, soluble aluminum, and cerium. The oxide inclusions in the electrode with 0.300 mass% Ce are CeS and Ce2O2S. These CeS inclusions were removed by molten slag adsorption during the ESR. A part of these Ce2O2S inclusions was removed by slag adsorption, and the remaining entered into the liquid metal pool. The oxide inclusions in the liquid metal pool and the ingot were Ce2O3 and Ce2O2S. The Ce2O3 inclusions were formed through the chemical reaction between the soluble oxygen and cerium in the liquid metal pool. The Ce2O2S inclusions in the liquid pool originate from reoxidation products during the ESR process and the relics from the electrode.