This investigation elucidated the effects of C and Cr content on the high-temperature microstructures of Fe-9Al-30Mn-xC-yCr alloys by means of optical microscopy and transmission electron microscopy. With increasing Cr content, the phase transition sequence within the α phase was found to be α + B2 → α + B2 + DO3 → α + DO3. And with increasing C content, a γ → (γ + κ) phase transition was observed within the γ phase. The κ phase carbides ((Fe,Mn)3AlCx) had an ordered L′12-type structure with lattice parameter a = 0.368 nm and were formed by a spinodal decomposition during quenching. The amounts of Cr7C3 increased with the C and Cr content. Moreover, the Al and Mn content played important roles in expanding the (α + γ) region. These features have not been previously reported in the Fe-Al-Mn-C-Cr alloy system.
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