Influence of Sulfur on the Plasma Decarburization and Desulfurization of Corrosion-Resistant Steels

Analysis of the kinetics of the processes occurring in the area of interaction between a plasma torch and Fe–Cr–S, Fe–Cr–Ni–S melts has been based on the influence of sulfur on the decarburization and desulfurization upon treatment of the melts by oxidizing plasma. The kinetic parameters of the plasma decarburization of high-chromium melts is determined, and the influence of the partial oxygen pressure in a plasma-forming gas and the sulfur content in a metal is established. At a low sulfur content in a metal in melting of Fe–Cr–S, Fe–Cr–Ni–S alloys in argon plasma, the limiting stage of desulfurization is found to be either sulfur evaporation in a plasma spot or its diffusion from the melt volume to the interface. Both processes are described by first-order equations. During treatment of a melt by an oxygen-containing plasma, sulfur is mainly removed due to the formation of gaseous oxides. At a high sulfur content in a melt, desulfurization takes place in the sorption kinetic mode. Under these conditions, the process rate decreases and the reaction can approach the second order. At increase in oxygen content in a plasma-forming gas intensifies decarburization and desulfurization; however, the rate constant is mainly determined by the initial sulfur content in a metal and, then, by the partial oxygen pressure in the gaseous phase.