The Solubility of Nitrogen and the Equilibrium of Nb-Nitride Forming Reaction in Liquid Fe-Nb Alloys

Solubility of nitrogen and equilibrium of Nb-nitride forming reaction in liquid Fe-Nb alloys under the presense and the absence of Nb-nitride were measured by the sampling method at 1600°, 1650° and 1700°C in the concentration range of 0∼30%Nb, and the behaviors of niobium and nitrogen were thermodynamically discussed through these experimental results.The solubility of nitrogen markedly increased with increasing niobium concentration in liquid alloy in the absence of Nb-nitride, and it decreased with increasing temperature especially at a higher concentration of niobium. On the other hand, it decreased with increasing niobium concentration in the presense of Nb-nitride. The interaction coefficient of niobium, fN(Nb) can be expressed as a function of niobium concentration at each temperature as follows:(This article is not displayable. Please see full text pdf.) The Nb-nitride appeared in the liquid Fe-Nb-N system was confirmed to be a hexagonal and cubic NbN by Debye-Scherrer X-ray diffraction analysis. The standard free energy of decomposition of NbN was determined to be(This article is not displayable. Please see full text pdf.) The self-interaction parameter of niobium, eNb(Nb) was also estimated as zero. The empirical equations for estimating the solubility limit of niobium when the nitride begins to form in liquid Fe-Nb alloys under a given nitrogen pressure were obtained as follows:(This article is not displayable. Please see full text pdf.)