Nitrogen Solubility in Liquid Fe-Nb, Fe-Cr-Nb, Fe-Ni-Nb and Fe-Cr-Ni-Nb Alloys

The N-containing Fe-Cr-Ni-Nb austenitic heat-resistant steels have become the research focus of high-temperature material. Nitrogen plays an important role on the strength and structural stability of the steels, and thus the accurate control of nitrogen content is of great significance to the smelting process. In this paper, the nitrogen solubility in liquid Fe, Fe-Nb, Fe-Cr-Nb, Fe-Ni-Nb and Fe-Cr-Ni-Nb systems from 1 823 to 1 873 K were investigated by gas -liquid metal equilibrium experiments. In liquid Fe-Nb system with a niobium content of 5 to 20%, the solubility of nitrogen increased with niobium content. The first-order interaction parameter of niobium on nitrogen at 1 873 K and its relationship with temperature were determined as follows: e(N(1 873K))(Nb) =-0.0672, e(N)(Nb) = -375.6 / T + 0.133. In the liquid Fe-Cr-Nb and Fe-Ni-Nb systems, the second-order cross-interaction parameters of chromium or nickel with niobium on nitrogen were determined as follows: gamma(Cr,Nb)(N) = 36.2/T -0.01728, gamma(Nt, Nb)(N) = 4.59/T -0.00187. Furthermore, a more accurate nitrogen solubility prediction model for the liquid Fe-Cr-Ni-Nb system was established based on the existing thermodynamic parameters and the interaction parameters obtained in this study.