Phase transformation of the L12 phase to kappa-carbide after spinodal decomposition and ordering in an Fe-C-Mn-Al austenitic steel

Fe-C-Mn-Al steels have the potential to substitute for commercial Ni-Cr stainless steels. For the development of Fe-C-Mn-Al stainless steels, phase transformations play an important role. Our methods of studying the phase transformations of the steel include heating, cooling, and/or annealing. The results of our study show that spinodal decomposition, an atomic ordering reaction and the transformation of the L12 phase to kappa-carbide occur in the Fe-C-Mn-Al steel. After cooling, the austenite decomposes by the spinodal mechanism into solute-lean and solute-rich austenite phases. The solute-rich austenite phase also transforms into the L12 phase via the ordering reaction upon cooling to lower temperatures. After quenching and prolonged annealing, the L12 phase grows in the austenite and finally transforms into kappa-carbide. This L12 phase to kappa-carbide transformation has not been observed previously.