The effect of the intercritical annealing temperature on the phase transformations during heat treatment of a 0.17C-1.46Mn-0.26Si-1.81 Al-0.01P (mass contents in %) TRIP steel has been investigated via dilatometric measurements, X-ray diffraction measurements and ther-modynamic analysis. As indicated from thermodynamic analysis, this steel has a wide austenite/ferrite two-phase co-existing region and therefore the effect of intercritical annealing temperature is pronounced. During the heat treatment, the intercritical annealing temperature is selected to be 1073 K, 1173 K, 1273 K and 1373 K, at which temperatures the equilibrium austenite fraction varies from 0.25 to 0.56. After intercritical annealing the samples are quenched to 673 K at a rate of 20 K/s, and held there for 120 s in order to observe bainitic transformation. All phase transformations, including austenite transformation, ferrite formation, bainite formation, cementite formation and dissolution as well as martensitic transformation, are involved in this investigation. From the dilatometric data, it is found that with increasing intercritical annealing temperature more austenite transforms to ferrite or bainite during cooling or during the isothermal holding at 673 K. XRD results reveal that almost the same amount of austenite with similar stability is retained at room temperature, irrespective of the intercritical annealing temperature. From the results, one can conclude that changing intercritical temperature does not significantly influence the TRIP effect.
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