Measurement of volume fraction of ε martensite in Fe–Mn based alloys

In this work, we propose a new way of measuring the volume fraction of ε martensite in Fe–Mn based alloys. Since the specific volume of ε, depending on alloy composition, is smaller than that of ɣ, volume expansion (VE) takes place on ε → ɣ reverse transformation. The amount of the volume expansion is proportional to the product of specific volume difference times the volume fraction of ε martensite, therefore, the measurement of two former values leads to the volume fraction. Two Fe–Mn based alloys are taken as examples, an Fe–21Mn and an Fe–32Mn–6Si alloys which undergo ɣ → ε on cooling and by cold rolling, respectively. Thus, former alloy has isotropic ε, the latter has anisotropic ε.