High-temperature stability of retained austenite and plastic deformation mechanism of ultra-fine bainitic steel isothermally treated below Ms

The mechanical properties of the sample and the stability of retained austenite were studied by designing two kinds of ultra-fine bainitic steel with different heat treatment methods (austempering above and below Ms (martensite start temperature)), which were subjected to tensile tests at 20 and 450 °C, respectively. The results show that compared to room temperature (20 °C) tensile properties, the uniform elongation of the sample at high temperature (450 °C) significantly decreased. Specifically, the uniform elongation of the sample austempered above Ms decreased from 8.0