Investigation of the Effect of Annealing Temperature on Flow Behavior of Constituent Phases in a Duplex Lightweight Steel Based on Inverse Analysis

This study investigates the effect of annealing temperature on the flow behavior of constituent phases in a Fe-12Mn-8Al-0.8C (wt.%) duplex lightweight steel. The mechanical property parameters of the samples annealed at 1000 °C (A1000) and 1200 °C (A1200) were obtained by combining experiments (microstructure characterization and nanoindentation tests) and inverse analysis. Upon annealing from 1000 to 1200 °C, the elastic moduli of ferrite and austenite decreased by ~20 and ~14 GPa, respectively; the yield strength of austenite dropped from 658.5 to 471.9 MPa while that of ferrite remained nearly unchanged (751.8 to 735.4 MPa); and the strain-hardening exponents of austenite and ferrite decreased from 0.239 and 0.183 to 0.191 and 0.175, respectively. A flow stress reversal between the constituent phases occurs in A1000, whereas a large flow stress difference is maintained in A1200. The macroscopic true stress-strain curves were predicted by the isostrain method (ISM) and non-isostrain method (NISM). Both methods accurately predict the flow stress for A1200, while for A1000 the accuracy of ISM is lower than that of NISM. This is attributed to the difference in phase volume fraction and the additional strengthening effect from the flow stress reversal in A1000.