STRUCTURE AND THERMODYNAMICS OF NIOBIUM NITRIDE IN EQUILIBRIUM WITH LIQUID FE-NB-N ALLOY

From the viewpoint of a fundamental study of steelmaking, the direct determination of the structure of niobium nitride in equilibrium with liquid Fe-Nb-N alloy has been carried out by a temperature x-ray diffraction technique. It was found that niobium nitride equilibrating with liquid Fe-(10 to about 20) mass% Nb-N alloy at 1813 K under a nitrogen pressure of 0.2 to about 0.6×105 Pa existed as the δ phase with fcc structures. From both the lattice parameter and the thermodynamic analysis it is estimated that the composition of the niobium nitride at 1813 K changes monotonously from NbN0.8 to NbN0.9 with the variation of nitrogen pressure from 0.2×105 to 1.0×105 Pa.