Kinetics of nitrogen absorption and desorption in high-Cr molten steel under pressurized atmosphere

Abstract

The rates of nitrogen absorption and desorption in high-Cr molten steel under a pressurized atmosphere were investigated using a pressurized directional solidification furnace. In this study, the melting experiments were performed under a maximum gas condition of 1.0 MPa. It was found that nitrogen absorption rate took the same value under the conditions of unified partial pressure on N2 gas in spite of the different total pressure. The mass transfer coefficient in the liquid phase of high-Cr molten steel at 1 823 K was estimated as 0.0009 m·s-1. On the other hand, it was found that the rate constant at the gas/liquid interface for the nitrogen desorption reaction decreased with the increase of nitrogen partial pressure. This result indicates that the nitrogen activity in the molten steel has an influence on the chemical reaction at the gas/liquid interface. Furthermore, the mass transfer coefficient in the gas phase decreased with the increase of total pressure. As numerical kinetic analysis shows, this result suggests that mass transfer in the gas phase is very important for the nitrogen absorption and desorption reactions under a pressurized atmosphere.