Dissolution Behavior of Ferritic Stainless Steel in Liquid Magnesium

Abstract

Steel containers and equipment are used to handle Mg and Mg-alloy melts in industrial processes such as Mg casting and Ti smelting. In this study, the dissolution behavior of SUS430 ferritic stainless steel in liquid Mg was quantitatively evaluated in order to obtain fundamental information on the contamination of Mg with steel materials in these industrial processes. Pure Mg was sealed in a SUS430 crucible and melted at 1073–1273 K for 24–96 h. In addition to Fe and Cr, some minor elements in the SUS430 (Mn, Ni, and Cu) were evaluated as impurity elements dissolved in liquid Mg. The concentrations of Fe and Cr in liquid Mg reached a steady state within 24 h, and the empirical equations describing their temperature dependence were obtained. In contrast, the concentrations of Mn, Ni, and Cu in Mg increased with increase in melt holding time. With the dissolution of these elements, a region with Mn concentration lower than that of the original composition was formed on the inner wall of the SUS430 crucible. The validity of the experimental values of impurity concentration in Mg was discussed based on the thermodynamic data of Mg–i (i = Fe, Cr, Mn, Ni, and Cu) binary systems and SUS430. Furthermore, impurity uptake through liquid Mg during Ti production using the Kroll process was preliminary discussed. The findings of this study provide important and beneficial information for improving impurity control in the melting and casting of Mg and in Ti smelting using Mg as a reductant.