The influence of temperature on sigma-phase formation and the resulting hardening of Fe-Cr-Mo-alloys

Hardening in Fe-Cr-Mo-alloys due to the formation of sigma-phase, has been the subject of theoretical and experimental interest. In the present invest igation Fe-Cr-alloys containing 0, 2, 4 and 6% Mo were prepared and were fu lly transformed to the sigma-phase by isothermally annealing the samples fo r various periods at temperatures of 600-800 degrees C. After each annealin g cycle room temperature CEMS-spectra were recorded and micro-hardness test s were performed. The micro-hardness increases with annealing time and temp erature, in accordance with the fraction of sigma-phase present, and ranged from about 140 HV to 200 HV. From the measurements, activation energies we re also deduced.