Effects of C and Cr content on high-temperature microstructures of Fe–9Al–30Mn–xC–yCr alloys

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.