Effect of the Slag Composition and a Protective Atmosphere on Chemical Reactions and Non-Metallic Inclusions during Electro-Slag Remelting of a Hot-Work Tool Steel

Abstract

The remelting behavior of the hot-work tool steel X37CrMoV5-1 is investigated with several experimental melts on a lab-scale ESR-plant. The investigated parameters comprise a variation of the slag compositions and the use of a protective nitrogen atmosphere. Variations of the slag composition include slags with different contents of CaF2, CaO, and Al2O3 as well as a variation of the SiO2-content in the slag. The remelted ingots are forged and analyzed regarding their chemical composition. The distribution and composition of the non-metallic inclusions (NMI) is studied by an automated SEM-EDX method. Additionally, the chemical composition of the slag after remelting is analyzed. The results show clearly an equilibrium reaction between Si and Al in the steel with SiO2 and Al2O3 in the slag as well as the effect of oxygen in open ESR operation. A protective atmosphere reduces the Si-losses during remelting, but has no major effect on the number or composition of NMI compared to open remelting. The content of NMI, especially the larger ones, is reduced significantly in all remelting experiments. The majority of the NMI are MA-spinel type except for the CaO-free slag, where alumina inclusions prevail. In general, remelting leads to an almost complete removal of sulfides, a reduction of oxisulfides, and a slight increase of oxides.