Control of MgO•Al2O3 Spinel Inclusions during Protective Gas Electroslag Remelting of Die Steel

The effect of calcium treatment and/or aluminum-based deoxidant addition on the oxygen control and modification of MgO center dot Al2O3 spinel inclusions during protective gas electroslag remelting (P-ESR) of H13 die steel with low oxygen content was experimentally studied. It is found that all the inclusions in the consumable electrode are MgO center dot Al2O3 spinels, besides a few MgO center dot Al2O3 spinels surrounded by an outer (Ti,V)N or MnS layer. After P-ESR refining combined with proper calcium treatment, all the original MgO center dot Al2O3 spinels in the electrode (except for the original MgO center dot Al2O3 spinels having been removed in the P-ESR process) were modified to mainly CaO-MgO-Al2O3 and some CaO-Al2O3 inclusions, both of which have a low melting point and homogeneous compositions. In the case of only Al-based deoxidant addition, all the oxide inclusions remaining in ESR ingots are MgO center dot Al2O3 spinels. The operation of Al-based deoxidant addition and/or calcium treatment during P-ESR of electrode steel containing low oxygen content is invalid to further reduce the oxygen content and oxide inclusions amount compared with remelting only under protective gas atmosphere. All the original sulfide inclusions were removed after the P-ESR process. Most of the inclusions in ESR ingots are about 2 mu m in size. The mechanisms of non-metallic inclusions evolution and modification of MgO center dot Al2O3 spinels by calcium treatment during the P-ESR process were proposed.