THERMODYNAMIC DATA OF THE FORMATION OF TITANIUM NITRIDE IN IRON

The solubility of titanium nitride in liquid iron is described by the solubility product log([%Ti][%/N])(l) = -17040/T + 6.40 reported by Tu rkdogan. The solubility in delta ferrite measured by Kunze is log ([%T i][%N])(delta) = -17205/T + 5.56. Combining the solubilities in both p hases and the solubilities of nitrogen the distribution equilibrium of titanium can be derived. It is characterized by the thermodynamic dis tribution coefficient k(o,Ti)(delta/l) = [%Ti](delta)/[%Ti](l) = 0.40. By zone melting and secondary ion mass spectrometry of the titanium d istribution k(Ti)(delta/l) = 0.53 was measured. An analysis (o)f all k nown data led to k(o,ti)(delta/l) = 0.40...0.50. Measurements of the T iN solubility in austenite by heat treatment were not significant. The y led to distribution coefficients between 0.07 and > 1, By zone melti ng in a carburizing atmosphere a distribution coefficient k(Ti)(gamma/ l) = 0.12 was measured. from a thermodynamic analysis performed by Oht ani et al., from the TiN solubility in the melt, and from the solubili ties of nitrogen k(o,Ti)(gamma/l) = 0.13 was deduced. Basing on the di stribution equilibria of titanium and nitrogen and on the measured tem perature dependence the solubility product log([%Ti][%N])(gamma) = -15 000/T + 4.06 was obtained.