The Effects of Si and Al Alloying on [alpha]/[gamma] Phase Equilibria in Fe-Cr-Ni-Mn Based Ternary and Quaternary Systems

Phase equilibria between the ferrite phase ([alpha]) and the austenite phase (γ) were investigated in the iron-rich corner of the Fe-Cr-Mn-Ni-Si/Al systems at 1000 °C using a diffusion multiple approach and scanning electron microscopy/energy dispersive spectroscopy (SEM/EDS) techniques. Cr equivalents of Si and Al are established as a function of Ni and Mn content in contrast to fixed values reported in other studies. The Cr equivalents of Si (Cr^sub eq^^sup Si^) are in the range between -0.5 and 1.3 being positive at 0 wt.% Mn and with values slightly below zero at 5-15 wt.% Mn. The Cr equivalents of Al (Cr^sub eq^^sup Al^) ranged between 0.6 and 4.8 decreasing with increase in Ni and Mn content. When compared to Cr^sub eq^^sup Al^, the Cr^sub eq^^sup Si^ do not show a strong dependence on Ni and Mn content. Thermodynamic calculation using Thermo-Calc software agrees with the experimental results qualitatively.