A Eutectoid Reaction for the Decomposition of Austenite into Pearlitic Lamellae of Ferrite and M23C6 Carbide in a Mn-Al Steel

Abstract

We discovered a eutectoid reaction in an Fe-13.4Mn-3.0Al-0.63C (wt pct) steel after solution heat treatment at 1373 K (1100 °C) and holding at temperatures below 923 K (650 °C). The steel is single austenite at temperatures from 1373 K to 923 K (1100 °C to 650 °C). A eutectoid reaction involves the replacement of the metastable austenite by a more stable mixture of ferrite and M23C6 phases at temperatures below 923 K (650 °C). The mixture of ferrite and M23C6 is in the form of pearlitic lamellae. The morphology of the lamellae of the product phases is similar to that of pearlite in steels. Thus, we found a new pearlite from the eutectoid reaction of the Mn-Al steel featuring γ → α + M23C6. A Kurdjumov–Sachs (K-S) orientation relationship exists between the pearlitic ferrite (α) and M23C6 (C6) grains, i.e., (110)α // (111)C6 and [\( \overline{1} \)11]α // [0\( \overline{1} \)1]C6. The upper temperature limit for the eutectoid reaction is between 923 K and 898 K (650 °C and 625 °C).