The age-hardening response of martensitic structures of Fe-Ni-Mn ternary alloys was studied in relation to their dilatation, microstructures and the results of X-ray diffraction tests.
Age-hardening was observed at 450°∼500°C in the decomposition process of metastable, supersaturated Fe-Ni-Mn martensitic structures in the egg-shaped region around the composition of 12%Ni and 6%Mn. In this region, the increment of hardness was measured as 10∼12 in Rockwell-A scale, and the Ms points of alloys were observed at about 100°C.
It was concluded that the hardening occurred due to the internal strain caused by the compositional fluctuation in the matrix as in the case of Fe-Ni-Co alloy or by the precipitation of NiMn phase (bcc).