High-strength Fe-20Mn-Al-C-based Alloys with Low Density

Mechanical properties of Fe-20Mn-(10-14)Al-(0-1.8)C (mass%) quaternary and Fe-20Mn-(10-14)Al-(0.75-1.8)C-5Cr (mass%) quinary alloys were investigated by hardness, cold-workability and tensile tests at room temperature. The gamma(fcc) alloys in both quaternary and quinary systems with a low density of less than 7.0 g/cm(3) showed an excellent ductility and their hardness and tensile strength increased with increasing Al and C contents. The gamma+alpha(bcc) duplex alloys also exhibited a high tensile strength by controlling the alpha volume fraction. TEM observation confirmed that high hardness and tensile strength of the alloys with high Al and C contents are caused by the precipitation of nano-size kappa-carbide with perovskite structure during cooling from the annealing temperature. Fe-20Mn-11Al-1.8C-5Cr alloy with a density of 6.51 g/cm(3) showed a high specific strength of more than 180 MPa . cm(3)/g with a good tensile elongation of 40%. The present Fe-20Mn-Al-C(-5Cr) alloys showed a higher specific strength than conventional steels.