Interactions Between Metal and Slag Melts: Steel Desulfurization

Abstract

Knowledge of the partitioning behavior of sulfur between molten metals and silicates is of interest for understanding processes in the early solar system and in the deep Earth at the mantle/core boundary, but also in technical applications such as the production and purification of steel. Thermodynamic aspects relevant to processes in the Earth and in the early solar system are presented by Baker and Moretti (2011) and Ebel (2011) of this review volume. Here we focus on interactions between molten metals and slags which are the basis for desulfurization of molten metals during steel production. Desulfurization is an important step in the refining of high-quality steels for various applications. The production of liquid steel can be described schematically as follows. Steel can be produced directly from iron ore which is reduced to hot metal in a blast furnace (BF) or by melting scraps in an electric arc furnace (EAF). The hot metal is transformed into steel by oxidizing dissolved carbon in a basic oxygen furnace (BOF). During this process, the phosphorus content is reduced as well. Before the BOF operations, a first desulfurization is performed in the transfer vessel from BF to BOF. After scrap melting or refining in the BOF, steel is “tapped” in a ladle for secondary steelmaking operations, i.e., further decarburization (especially for Ultra-Low Carbon steels), deoxidation (to reduce the oxygen content), alloying (to reach the target composition) and further desulfurization, if needed. In solid steel, sulfur is mainly present as manganese sulfide (MnS) inclusions. MnS inclusions affect the processing and properties of steel. Their volume fraction, size, shape and distribution depend on many factors. The most important factors are the S-content, the solidification rate, the degree of hot and cold deformation and the hot working temperatures. Since the inclusions are more plastic than steel, they act …