In this study, the evolution of microstructure and mechanical behavior in medium manganese steel subjected to double intercritical annealing was investigated. Austenite reversion transformation (ART) occurred during both single (730°C) and double intercritical annealing (700°C and 750°C). A complex ultrafine microstructure consisting of three phases—retained austenite, martensite, and ferrite—with fine carbides was formed after single annealing. Following double annealing at 700°C, the martensite generated during the first intercritical annealing reverted to austenite, resulting in the maximum stabilized austenite fraction and a final microstructure composed mainly of ferrite and retained austenite. When the second annealing temperature was increased to 750°C, a larger amount of austenite was formed; however, its reduced thermal stability caused partial transformation into martensite. Double intercritical annealing thus produced multiple populations of austenite and ferrite/martensite phases with varying thermal and mechanical stabilities, enhancing the overall mechanical performance. The strength was maximized after high‐temperature (750°C) double annealing, whereas elongation and ductility were optimized at the lower annealing temperature (700°C).
Franceschi et al. (Tue,) studied this question.