Effect of aging on the microstructure and tensile properties of Fe-Ni-Mn-Cr maraging alloys

Effect of aging on the microstructure and mechanical properties of chromium-containing Fe-Ni-Mn maraging alloys was studied. An Fe-10Ni-7Mn-2Cr (wt.%) alloy exhibited strong age hardenability but suffered from premature intergranular brittleness after aging. Further chromium addition resulted in partial austenite retention in Fe-10Ni-7Mn-6Cr (wt.%) and Fe-10Ni-7Mn-9Cr (wt.%) alloys at ambient temperature. The retained austenite exhibited mechanical instability during tensile loading at ambient temperature and transformed into martensite substantially, aiming at large tensile ductility. Age hardenability of the studied alloys decreased by increasing of retained austenite. In an Fe-10Ni-7Mn-6Cr (wt.%) alloy, transmission electron microscopy studies represented pronounced precipitation of a face-centered tetragonal (fct) θ-NiMn intermetallics in martensite and weak precipitation of a needle-shaped phase in retained austenite. After aging of the partially transformed alloy, yield strength increased moderately while tensile ductility decreased drastically. The ductility loss is mainly attributed to the premature intergranular fracture initiating within the aged martensite.