Fig. 2(a) shows an electropulsed Fe-26Mn-9Al-0.75C sample after
cold rolling to 70% reduction. No cracks were detected from the optical
observation. In comparison to those not electropulsed samples, as
shown in Fig. 1(a), the formability of electropulsed sample has been improved
considerably. To identify the causes of the improvement, the microstructure
was analysed by SEM. Fig. 2(b) presents a SEM micrograph
of the electropulsed samples. The grey particles in the image are κ-
carbides. The previous lamellar κ structure has been converted into
sub-micron particulate structure. The average particle size is 250 nm.
Image analysis using Image J software reveals that κ volume fraction
has been reduced from 14% to 6.8% in the overall sample and from
68% to 31% in some local areas by the electropulsing treatment.
TEM analysis for Fe-26Mn-9Al-0.75C samples before and after
electropulsing treatment is presented in Fig. 3. Fig. 3(a) and 3(c) show
lamellar κ structure in the samples without electropulsing.
Fig. 3(b) and 3(d) show particulate κ structure after electropulsing
treatment. The α-matrix structure is also refined significantly. The average
α grain size after electropulsing is 1.46 μm. As discussed in Section 2,
the spheroidized and refined κ microstructure leads to the improvement
of formability. SADP in Fig. 3(e) and the orientation marks in
Fig. 3(f) prove that the orientation relationships between κ and α ferrite
are unchanged by the electropulsing treatment.