An investigation into the zone formation in a Fe-31Mn-8Al-0.67c austenitic steel has been made using resistivity and thin foil technique.
The electrical resistivity during zone formation shows a characteristic peak. Aging at a range of temperature enabled the activation energy of zone formation determined and gave activation energies closed to 1.17eV.
By means of TEM micrographs and electron diffraction pattern, plate-shaped G.P zones of about 20-50Å in size were observed in the matrix of the specimen aged 2 hours at 550℃.
Also for the specimen aged at 550℃ for 168 hours, equilibrium $K[(Fe, Mn)_3AlCx]$ Phase was observed in the $\gamma$ phase matrix and grain boundary. At 550℃, the decomposition sequence of the $\gamma$ phase was : $\gamma$(fcc)→G.P zone→K'(metastable phase)→K'+K(equilibrium phase) ---→ K.
For the alloy aged at 550℃ and 500℃, the microhardnes VS. aging time curve exhibit two peaks typical of age hardening curve. For the alloy aged at 600℃, the microhardness curve exhibit single peak.
