Study on the relationship between vacuum denitrification and manganese evaporation behaviours of manganese steel melts

Abstract Herein, the manganese evaporation and denitrification behaviours of manganese steel melts with various initial manganese and nitrogen contents, refining times, and vacuum conditions were experimentally investigated. Thermodynamic and kinetic analyses were performed to evaluate the interaction mechanism between manganese evaporation and denitrification. The results indicated that the denitrification process was in good agreement with 1.5th-order reaction kinetics, while the denitrification process followed 1st-order and 2nd-order reaction kinetics under high final pressure and high initial nitrogen content, respectively. The denitrification rate constant significantly increased with increasing initial nitrogen content. Furthermore, it was found that a high initial nitrogen content can promote manganese evaporation, which is attributed to the partial demanganisation reaction proceeding at the nitrogen bubble–metal interface. Moreover, denitrification is blocked by an increase in the manganese content in the steel melt, which is related to the strong affinity between nitrogen and manganese atoms, consistent with thermodynamic calculations. Ultimately, it was found that moderately increasing the pressure and reducing the refining time can both rapidly remove nitrogen and slow down manganese evaporation. This work provides a theoretical basis for the vacuum melting of manganese steel with high cleanliness.