Size distribution of martensite plates in an Fe-Ni-Mn alloy

In this paper, the size distribution of the martensite plates in an Fe-23.2 Ni-2.81 Mn (wt%) alloy, which transforms isothermally at subzero temperatures, is reported. The distribution of the martensite plates has been determined as a function of the reaction temperature, volume fraction of martensite, the austenitic grain size, a superimposed elastic stress and prior plastic strain (at room temperature) of austenite. Increasing the driving force either by decreasing the reaction temperature or by a superimposed elastic stress changes the size distribution by enhancing the extent of radial growth of the martensite plates. Pre-straining of austenite does not allow the martensite plates to grow to the full extent. The present results show that the radial growth of the martensite plates increases with increasing driving force and decreases due to work-hardening of austenite. The transformation is found to progress through a combination of the spreading-out of clusters and filling-in of pockets, both occurring simultaneously. However, the extent of filling-in, i.e. compartmentalization of austenite grains, is more in the coarse-grained (0.09 mm) and medium-grained (0.048 mm) specimens compared to that in the fine-grained (0.019 mm) specimens.