THERMODYNAMIC ANALYSIS OF THE DELTA-FERRITE IN THE SYSTEMS FE-CR-N AND FE-CR-MN-N

The solubility of nitrogen in ferritic iron-chromium alloys with mass contents of between 6.08 to 23.94% chromium was measured in the temper ature range 1523 to 1773 K. Combining the results with published data for the nitrogen solubility in iron-chromium, improved parameters desc ribing the chromium-nitrogen interaction were derived. The Gibbs free excess energy can be described by <(G)over bar (E)(N)> (Cr) = (-773000 +91.0211 . T). gamma(Cr) + (983800-208.705 . T).gamma(Cr)(2) - 220200 .gamma(Cr)(3). Calculations of the nitrogen solubility using this equa tion and calculations using parameters published by the Swedish Instit ute of Metals Research differ the more the higher the temperature. A r epeated analysis of measurements of the nitrogen solubility in ferriti c Fe-Cr-Mn alloys using the Gibbs free excess energy derived in this i nvestigation for the chromium-nitrogen interaction leads to the mangan ese-nitrogen interaction energy <(G)over bar(N)(E)>(Mn)+<(G)over bar(N )(E)>(Cr,Mn)=(-668200+262.801 . T). y(Mn)-596500 . y(Mn)(2)+617900 y(M n)(3)+3/2y(Mn)(2)y(Cr)+1/2y(Mn)y(Cr)(2))-326100 . y(Cr)y(Mn).