The martensitic transformation of retained austenite in a 0.20C-1.52Mn-0.25Si-0.96Al (mass contents in %) TRIP steel is investigated using thermo-magnetic measurements in the temperature range between 300 K and 5 K at a constant magnetic field of 5 T. In addition, the transformation is studied by X-ray diffraction and thermodynamic analysis. From the difference of magnetisation during heating and cooling processes the temperature dependent austenite fraction is determined, which fits well with the prediction from a thermodynamic model. It is also found that nearly all austenite transforms athermally to martensite upon cooling to 5 K and the transformation start and finish temperatures are 355 K and 114 K. The measured thermal stability is related to the carbon concentration of individual austenite grains.
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