Abstract: In order to study the thermal stability of retained austenite in the cold-rolled transformation induced plasticity (TRIP) steel, thermal decomposition of retained austenite in a cold-rolled TRIP steel sheet with the composition of 0.25C-1.78Mn-1.23Al-0.54Cu- 0.33Ni is investigated by means of differential scanning calorimetry(DSC). The decomposition temperature and the activation energy of the retained austenite in TRIP steel are measured by the Kissinger method, and the decomposition temperature is higher than those of quenched steels. The kinetic parameters n and A are obtained by JMA equation, which are used to predict thermal decomposition kinetic of retained austenite in TRIP steel during isothermal transformation. The results show that the retained austenite has a high stability when bainite isothermal transformation temperature is 420 ℃, there is still more than 90% of the retained austenite without decomposing even if the bainite isothermal transformation time is 600 s. The results also show that the amount of retained austenite predicted by JMA equation agrees well with the actual value measured by X ray diffraction (XRD) when bainite isothermal transformation temperature is 420 ℃.

Key words: Differential scanning calorimetry, Isothermal transformation, Johnson-Mehl-Avrami equation, Retained austenite, Thermal stability, Transformation induced plasticity