The homogenization treatment is shown to have profound effects on the decomposition of austenite, suppression of microstructural banding, and work-hardening capacity of transformation-induced plasticity (TRIP) steels. Due to the similarity in the activity of carbon in different parts of the parent austenite phase and its extremely coarse grain size, a nearly full homogenization annealing results in the massive-like transformation during subsequent decomposition of austenite at slow cooling rates.
The room-temperature stability of the retained austenite against strain-induced martensitic transformation, its deformation behavior, the response to the bainitic isothermal treatment, the appearance of yield point elongation and other peculiarities of plastic flow, and the mechanical properties of transformation-induced plasticity (TRIP) steel were tailored based on the chemical homogeneity and the relative distribution of the retained austenite, bainite, and ferrite in the microstructure. The presence of ferritic-pearlitic banded structure in the initial microstructure resulted in an inhomogeneous TRIP microstructure, in which the retained austenite and bainite were confined to some bands and it was found to be responsible for the resultant inferior mechanical properties. The appearance of discontinuous yielding for the chemically inhomogeneous material was related to the martensitic transformation of unstable retained austenite at the initial stage of tensile deformation. These results are essential for better understanding of the behavior of advanced high-strength steels and their applications.
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