Interpretation of the abnormal high-temperature flow behavior of Fe-Mn-Al duplex lightweight steel

Abstract

The hot deformation behaviors of two Fe-Mn-Al lightweight steels were investigated by hot compression tests on a Gleeble-3500 thermal simulation machine over a practical range of temperatures and strain rates. Optical microscope (OM) and electron backscattered diffraction (EBSD) were carried out to observe the microstructural mo rphologies of samples after hot deformation. Different from the single austenite steel, the hot compression tests of the duplex steel were actually carried out on an austenite/δ-ferrite duplex matrix with various phase compositions. At the commencement of deformation, strain was intensively distributed in δ- ferrite due to its higher stacking fault energy (SFE), and the dynamic softening behavior occurred earlier in δ-ferrite than in austenite during the whole hot deformation period. As a consequence, the prior dynamic recovery (DRV) in δ-ferrite caused the yield-like behavior, and the strain partitioning between δ-ferrite and austenite resulted to a visible serration on the flow curves. The dominant continuous dynamic recrystallization (CDRX) in δ-ferrite at high temperature caused a typical dynamic recovery characteristic, and the dominant discontinuous dynamic recrystallization (DDRX) in austenite at low temperature resulted in a typical dynamic recrystallization characteristic of the flow curves.