Thermodynamics of nitrogen solubility and AlN formation in multicomponent high Mn steel melts

Thermodynamics of nitrogen and AlN formation in multi-component liquid iron alloys containing Mn, Al, Si and C was investigated by the metal/gas and the metal/nitride/gas equilibration techniques under reduced nitrogen partial pressures in Ar–N2 gas mixture. The N solubility was measured in binary Fe–Mn and Fe–Si alloy melts, and ternary Fe–Mn–Si, Fe–Al–Si, Fe–Mn–C and Fe–Si–C alloy melts over wide composition range at 1773–1873 K. Using Wagner’s formalism, the effect of alloying elements on the N solubility was described as the first- and second-order interaction parameters as well as the second-order cross-product parameters. The validity of the interaction parameters determined in the present study was checked by measuring the N solubility and AlN solubility product for a typical TWIP steel composition melt of Fe-25% Mn-0.3% Si-0.6% C-Al at 1723–1873 K.