Effect of Revert Addition on the Nitrogen Removal From Liquid Superalloy During Vacuum Induction Melting Process: Experimental and Simulation Studies.

Impurity and non-metallic inclusions control are imperative for the metallurgical quality of superalloys. In this paper, the effect of revert addition on the nitrogen removal and inclusion characteristics of GH4738 superalloy has been investigated. And a multiscale transient model for describing and predicting nitrogen removal from liquid superalloy during the refining process is developed by coupling macroscopic phenomena (including electromagnetic, fluid flow, heat, and mass transfer). A series of experimental data validate the reliability of the model. Results demonstrated that revert addition significantly suppressed the nitrogen removal efficiency and led to more nitrogen residue in the liquid superalloy, contributing to more nitrides or carbonitrides precipitation. The transient model shows that the residual nitrogen in the molten bath is spatially inhomogeneous distributed, in which the mass transfer of nitrogen between the gas–liquid interface is synergistically controlled by chamber pressure, bath temperature, and melt flow pattern. Increasing the refining power enhances the stirring intensity, which accelerates solute transport and facilitates nitrogen removal, but it also leads to a higher refining temperature that thermodynamically inhibits the denitrification reaction. Simulation results show that vacuum refining of revert superalloys by reducing the chamber pressure and increasing the metal bath stirring intensity is beneficial to obtain alloys with low nitrogen content. Considering the inhibitory effect of high temperature and revert addition, adjusting the refining power is recommended to promote nitrogen removal when the proportion of revert is more than 40 pct. [ABSTRACT FROM AUTHOR]