Martensitic transformation temperatures and microstructural features of FeMnCr Alloys

Abstract
FeMn based alloys are a low cost alternative to traditional SMAs due to their convenient one-way shape memory effect. While alloy systems containing several elements have received considerable attention along the last few years, namely FeMnSiCr, FeMnSiCrNi and modifications of these two containing precipitates, there is still scarce information about some of the related ternary systems. An important example is the FeMnCr system. Information about phase stability and transformation temperatures in this ternary system would be useful as input data for higher order alloy design. We present experimental fcc/hcp martensitic transformation temperatures of selected FeMnCr alloys measured by means of dilatometry and electrical resistivity. We have found that these transformation temperatures suffer an evolution when samples are thermally cycled, up to an asymptotic state. In the case of the studied samples, this asymptotic state is reached after a small number of cycles (n < 5). TEM observations aimed at elucidating the origin of this behavior found two main microstructural features: 1) the presence of very small precipitates in the alloy matrix, and 2) a tendency to form mono-oriented martensite inside each grain.