The oxidation behaviors of the austenitic Fe-8.7Al-29.7Mn-1.04C and duplex Fe-10Al-29Mn-0.4C alloys in air at elevated temperatures have been investigated by the X-ray diffraction and metallographic techniques. The results showed that the oxide nodules were formed on the surface of both alloys at 1073 and 1273 K during the early stage of oxidation. These oxide nodules grew and eventually coalesced to form continuous duplex scales. The composition and structure of the duplex scales depended on the oxidation temperature and alloy composition. For the duplex Fe-10Al-29Mn-0.4C alloy oxidized in air at 1073 K for 259.2 ks (72 h), the duplex scales consisted of an outer (FeMn)2O3 layer and an inner α-Al2O3 layer at the oxide-alloy interface. However, oxidation of the duplex Fe-10Al-29Mn-0.4C alloy at 1273 K for 259.2 ks led to the formation of an external (FeMn)3O4 and an inner α-Al2O3 layers with some internal oxides precipitated within the austenitic phase. Furthermore, the SEM micrographs showed that the oxide growth pits were formed on the austenitic Fe-8.7Al-29.7Mn-1.04C alloy after exposure in air at 1273 K for 259.2 ks. However, oxide pyramids were observed to grow on this alloy as the temperature was increased to 1473 K.
(Received November 6, 1986)
Keywords: oxidation, iron-aluminum-manganese-carbon alloy, duplex alloy, oxide nodule, oxide pyramid
* Institute of Materials Science & Engineering, National Sun Yat-Sen University, Kaohsiung, Taiwan, Rep. of China.