Kinetic Study of Mn Vacuum Evaporation from Mn Steel Melts

Abstract Considering the interference of Mn volatilization on the composition control during the vacuum treatment of medium/high Mn steel melt. The kinetic analysis of Mn volatilization from steel melt in various initial Mn contents, holding times, temperature and pressure regimes were investigated in lab scale experiments. The results show that Mn evaporation is accelerated significantly with the increase of temperature and initial Mn content in steel melt or with the decrease of chamber pressure. Furthermore, the logarithm of Mn content in steel melt has a linear function relationship with the holding time, indicating the first-order kinetic reaction of Mn evaporation. In addition, the overall mass transfer coefficient of Mn significantly decreases from 2.176E-05 to 5.932E-06 m s-1 with the increase of the initial Mn content from 2% to 30%. Moreover, high temperature and low partial pressure can obviously improve the overall mass transfer coefficient of Mn. Simultaneously, the apparent activation energy for Mn evaporation from steel melt is calculated to be 324.55 kJ mol-1. The theoretical kinetics model is established to fully analyze the evaporation mechanics of Mn, which is consistent with experimental results. In particular, with the increase of initial Mn content, the rate-limiting step transforms from mass transfer in the steel melt boundary layer to gas phase mass transfer, and mass transfer resistance in the gaseous phase is reached 91.22% with initial Mn content of 30%. Besides, the Mn evaporation process at high temperature and high partial pressure is determined by the mass transfer in the steel melt boundary layer and gas phase, respectively. This work systematically clarifies the factors influencing Mn loss in vacuum refining on high quality Mn steel manufacture.