Effects of microstructure and heat treatment on mechanical properties and corrosion behavior of powder metallurgy derived Fe-30Mn alloy

Microstructures, mechanical properties and corrosion rates (CR) of powder metallurgy derived Fe-Mn alloys have been investigated with respect to the particle size of the iron (Fe) powder and the extent of manganese (Mn) diffusion and alloying during sintering. By applying different heat treatments on Fe-30wt%Mn alloy, a phase transformation (γ → ε) for this composition and its influence on mechanical and corrosion properties have been studied. X-ray diffraction (XRD) and Transmission Electron Microscopy (TEM) have been conducted to characterize the transformation and identify the austenite (γ) and epsilon martensite (ε) phases in the system. Microstructures and tensile fracture surfaces were examined by Scanning Electron Microscope (SEM). The results show that the Fe particle size affects the overall Mn alloying significantly, i.e., coarse Fe particles (30-200 µm) result in Fe-Mn alloys with σy = 48.2 MPa, σu = 73.6 MPa, fracture strain of 2.42% and CR = 1.36 mmpy, while ultrafine particle size (< 44 µm) leads to σy = 134.2 MPa, σu = 215.8 MPa, fracture strain of 10.91% and CR = 0.29 mmpy. Heat treatments and formation of ε martensite have shown minor effect on tensile properties, but increased hardness and corrosion rate noticeably.