Strain rate response of mechanical behaviors for Fe-8Mn-6Al-0.4C duplex low-density steels with different austenite stabilities

Duplex low-density steels exhibit excellent mechanical properties under quasi-static tensile tests with the help of the transformation-induced plastic (TRIP) effect produced by the deformation-induced martensitic trans-formation (DIMT), which is sensitive to the strain rate. Therefore, adjusting the microstructure to accommodate the deformation at different strain rates is crucial for the optimal design of high-performance duplex low-density steels. In this study, Fe-8Mn-6Al-0.4C low-density steel was subjected to intercritical annealing (IA) treatment to obtain duplex microstructures with an inhomogeneous distribution of austenite grain sizes and tensile tests were performed at two strain rates. The response of the mechanical behavior to the strain rate was investigated, and the mechanical stability of austenite was evaluated using a method based on the grain size. The results show that the diverse mechanical behaviors of experimental steel depend mainly on the mechanical stability of austenite rather than the stacking fault energy (SFE). The mechanical stability of austenite increased with decreasing annealing temperature and was further enhanced by adiabatic heating at a higher strain rate. Accordingly, the DIMT mode changed from a stress-induced transformation to a strain-induced transformation until the DIMT was inhibited by adiabatic heating. The improvement in the mechanical properties of the experimental steel is attributed to the sustainable DIMT with a reasonable mechanical stability of austenite.