On the Eutectoid Reaction in a Quaternary Fe-C-Mn-Al Alloy: Austenite → Ferrite + Kappa-Carbide + M23C6 Carbide

Lamellae of ferrite, kappa-carbide, and M23C6 carbide are involved in a eutectoid reaction of an Fe-C-Mn-Al alloy after isothermal holding at temperatures below 923 K (650 °C). These lamellar phases are product phases from the decomposition of austenite during the eutectoid reaction of the quaternary alloy, i.e., austenite → ferrite + kappa-carbide + M23C6 carbide. Since the Al concentration in the steel is higher than that of the eutectoid composition, proeutectoid ferrite and kappa-carbide appear in the austenite prior to the eutectoid reaction to reduce the Al content of the retained austenite. The retained austenite decomposes into ferrite, kappa-carbide, and M23C6 carbide during the eutectoid reaction.