SOLUBILITY OF TITANIUM NITRIDE IN DELTA IRON

Titanium nitride in microalloyed steels can be formed already in delta iron, as can be shown by thermodynamical calculations basing on measurements of the solubility in austenite or in the melt. The solubility products calculated with respect to delta iron differ up to one order of magnitude. Therefore, between 1420 and 1510-degrees-C a direct measurement was performed on pure Fe-Ti-N alloys yielding a solubility product (related to the composition TiN1,0) of log L(TiN)alpha/delta = -17205/T + 5.56. It is identical with that one calculated from the solubility in liquid iron. The differing results of calculations basing on the solubility in austenite are attributed to incorrect data of the Gibbs free solution energy of titanium in austenite. Starting from the present measurements and from the data reported with respect to pure titanium and to the nitrogen solubility a Gibbs free solution energy G(Ti,gamma)H(x) - G(Ti,gamma)R = -40294 - 13.66. T[J/mole] was deduced which is more negative than previous data.