Thermodynamics of titanium and nitrogen in Fe-Si melt

The thermodynamics of titanium and TiN formation in Fe-Si-Ti-N melts was studied. A metal-nitride-gas equilibration technique was used to measure the activities of titanium and nitrogen in the presence of pure solid TiN under various nitrogen pressures in the temperature range of 1 843-1 923 K. The activity coefficients of titanium and nitrogen relative to 1 mass% standard state in liquid iron were calculated from the experimental results for Fe-Si alloys of silicon content up to 2.26 mass%. The first- and second order interaction parameters of silicon on titanium, e(Ti)(Si) and r(Ti)(Si), were determined as -0.0256 and 0 at 1 873 K, respectively. Similarly, the interaction parameters of silicon on nitrogen, e(N)(Si) and r(N)(Si), were determined as 0.0491 and 0 at 1 873 K, respectively. The temperature dependence of these interaction parameters was also determined. The validity of thermodynamic parameters determined in the present study was examined by observing the formation of TiN precipitates in a Fe-1%Si-Ti-N melt of controlled titanium and nitrogen contents at 1 873 K.