Characterization of microstructure formation and mechanical behavior of an advanced medium Mn steel

The response of a 0.1C-4.6Mn (wt.%) steel to ART annealing was investigated as a function of its initial microstructure, i.e. deformed (cold rolled) bainite-martensite structure or as-quenched (non-deformed) martensitic structure resulting from a subsequent austenitization treatment. Recrystallization and austenite transformation during annealing were characterized as a function of annealing temperature and time. Cold reduction accelerates the austenite formation and strongly influences the morphology of the resulting microstructure. Indeed, a fully polygonal microstructure is obtained when starting with a deformed microstructure, whereas lath-like and polygonal morphologies are observed after annealing of non-deformed martensite (double annealing). Tensile tests were performed after double annealing treatments followed by water quench. Only small evolution of tensile properties was detected as a function of holding time.