Abstract
A novel concept of microstructure design involving warm rolling and low-temperature annealing has been proposed to greatly improve the strength-ductility combination of medium Mn steel. The unique transformation induced plasticity has been triggered by firstly microbands and secondly deformation twins, enhancing the ductility significantly and the reasonable dislocation density in non-recrystallized austenite grains increases the yield strength greatly. The individual contribution of solid solution strengthening, grain boundary strengthening, V-precipitates strengthening and dislocation strengthening to yield strength is discussed by constitutive models, in which the tangled dislocation plays a dominant role. Best strength-ductility combination with yield strength (1239MPa), ultimate tensile strength (1341MPa), total elongation (41.8%) and product of strength and elongation (56.1GPa·%) has been obtained, which are comparable and superior to the reported medium-Mn steels.
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