Abstract: Thethermal induced γ εmartensitic transformation in a Fe 31 6 Mn 6 5 Si ( wt% ) alloy wasstudied by meansof X ray diffraction throughtwothermalcyclesin the83 480 Ktem perature range.Itisshownthatduringcoolingtheγ→εtransformationterminatesnotat TγNbutatalowertemperatureandtheγphaseexhibitsstrongstabilityevencoolingto83 K;like wise,εmartensiteis noticeably stable even heating up to 480 K. Atthe temperature about 275 K, an anomalousdecreaseintheintensityofthe(200)γreflections wasobserved on heat ing, whereasthe(101)εreflectionsshow ageneralvariationinintensity.Itisconsideredthat theabnormalphenomenonis probably related tothe magnetictransition of the γphase fromantiferromagnetism to paramagnetism .

Key words: Fe Mn, Fe Mn Sisystem , martensitictransformation, εmartensite