Fe-26Mn-9Al-0.75C samples (hereinafter to be referred as lower Mn
samples) are cracked severely after cold rolling. A representative OM
image for these samples is shown in Fig. 1(a). Fe-34Mn-9Al-0.65C samples
(hereinafter to be referred as higher Mn samples) however, have
no crack observed in their cold-rolled samples surface, as is illustrated
in Fig. 1(b). Both steels have the same Al but slightly different Mn compositions.
The higher Mn steel has better formability than that of the
lower Mn steel. SEM analysis reveals the microstructure of the samples,
as are presented in Fig. 1(c) for a lower Mn sample and Fig. 1(d) for a
higher Mn samples. Both samples are with lamellar structure despite
higher Mn sample demonstrates finer and more regular structure than
that of lower Mn samples. TEM selected area diffraction pattern
(SADP) results are presented in Fig. 1(e) for a lower Mn sample and in
Fig. 1(f) for a higher Mn sample. Based on the lattice parameter calculation
and crystal structure analysis, the lamellar phase in both steels is
found to be κ-carbide with lattice parameter 3.75 Å. The matrix in