Phase separation in Fe-Mn (20-40 wt % Mn) alloys

The structural changes produced in the Fe-40Mn and Fe-20Mn alloys by long-term isothermal heat treatment at temperatures from 600 to 1200°C are studied using x-ray diffraction analysis, transmission electron microscopy, and hardness tests. The results provide evidence, direct for Fe-40Mn and indirect for Fe-20Mn, that the Fe-Mn solid solution in these alloys undergoes phase separation in the temperature range studied. The conclusion is made that the solid-solution region in the Fe-Mn system, as well as in a number of other systems, is in fact a phase-separation region.