High-strength TRIPLEX light-weight steels having the generic composition, Fe-xMn-yAl-zC contained 18 to 28% manganese, 9 to 12% aluminium and 0.7 to 1.2wt%C. The microstructure comprised an austenitic γ-Fe(Mn,Al,C) solid-solution matrix possessing a fine dispersion of nano-sized K-carbides (Fe,Mn)3AlC1-x and α-Fe(Al,Mn) ferrite of various volume fractions. The calculated Gibbs free energy of the phase transformation γfcc → εhcp amounted to a free energy of 1.757kJ/mol, and the stacking-fault energy was deduced to be 110mJ/m2. This indicated that the austenite was very stable and no strain-induced ε-martensite was formed. Mechanical twinning was almost entirely inhibited during plastic deformation. The TRIPLEX steels exhibited a low density (6.5 to 7g/cm3) a strength of 700 to 1100MPa and total elongations of up to 60% or more. The specific energy absorption achieved at strain-rates of 103/s was about 0.43J/mm3.

Microstructures and Mechanical Properties of High-Strength Fe-Mn-Al-C Light-Weight TRIPLEX Steels. G.Frommeyer, U.Brüx: Steel Research International, 2006, 77[9-10], 627-33