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Nucleating Acicular Ferrite with Galaxite (Al2O3MnO) and Manganese Oxide (MnO2) in FeMnAlC steels

Effectiveness of galaxite (Al2O3MnO) and manganese oxide (MnO2) in nucleating acicular ferrite was demonstrated in a steel with composition of Fe-13.92Mn-4.53Al-1.28Si-0.11C. The hot rolled and quenched steel had a duplex microstructure of delta-ferrite and partially transformed austenite. Thermal treatments were used to manipulate the concentration and type of oxides and the ferrite plate density was found to correlate with inclusions of low misfit. Both bainitic and acicular ferrite were observed and the prior austenite had a grain diameter of 16.5 micrometers. Upon tensile testing the retained austenite transformed to alpha-martensite. Ultimate tensile strength and elongation were 970 MPa and 40 percent. The yield strength was found to be dependent on the ferrite plate size, which varied linearly with the strength of the austenite. Ductility decreased as the strength disparity between delta-ferrite and deformation-induced alpha-martensite increased.