Mechanical stability of retained austenite in aluminum-containing medium-Mn steel deformed at different temperatures

The thermal and mechanical stabilities of retained austenite in aluminum-containing medium-Mn 0.16C–4.7Mn–1.6Al–0.2Si sheet steel were investigated. The strain-induced martensitic transformation in Mn TRIP steel was studied at different temperatures. Static tensile tests were carried out at the temperature ranging from − 60 to 200 °C. The tests allowed to study the influence of the temperature on austenite-to-martensite transformation kinetics. The interrupted tensile tests and corresponding X-ray measurements of retained austenite amount were performed to determine the mechanical stability of retained austenite using the Sugimoto model. The microstructure changes were investigated using scanning electron microscopy (SEM), electron backscatter diffraction (EBSD), X-ray diffraction (XRD) and transmission electron microscopy (TEM) techniques. Observed results reflected the effects of deformation temperature on the mechanical stability of retained austenite and the corresponding response of this phase to martensitic transformation. It was found that an increase in the deformation temperature resulted in the reduced intensity of the TRIP effect due to the higher mechanical stability of retained austenite. At the highest deformation temperature (200 °C), the evidence of thermally activated processes affecting the mechanical behavior was identified.