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])₁ = ?17040/T + 6.40 reported by Turkdogan. The solubility in δ ferrite measured by Kunze is log<%Ti]%N])_δ = ?17205/T + 5.56. Combining the solubilities in both phases and the solubilities of nitrogen the distribution equilibrium of titanium can be derived. It is characterized by the thermodynamic distribution coefficient k^δ/I_o,Ti = %Ti]_δ/%Ti] = 0.40. By zone melting and secondary ion mass spectrometry of the titanium distribution k^δ/I_Ti = 0.53 was measured. An analysis of all known data led to k^δ/I_o,Ti = 0.40…0.50. Measurements of the TiN solubility in austenite by heat treatment were not significant. They led to distribution coefficients between 0.07 and > 1. By zone melting in a carburizing atmosphere a distribution coefficient k^γ/I_Ti = 0.12 was measured. From a thermodynamic analysis performed by Ohtani et al., from the TiN solubility in the melt, and from the solubilities of nitrogen k^γ/I_o,Ti = 0.13 was deduced. Basing on the distribution equilibria of titanium and nitrogen and on the measured temperature dependence the solubility product log(%Ti]%N])_γ = ?15000/T + 4.06 was obtained.