By controlling recrystallization degree: A plain medium Mn steel overcoming Lüders deformation and low yield-to-tensile ratio simultaneously

Abstract

A technical process concept, i.e., controlling recrystallization degree, was proposed and performed in order to manufacture the medium Mn steels overcoming discontinuous yielding and low yield-to-tensile ratio. Based on this, a plain medium Mn steel with 8.9 wt % Mn content was used in view of retarding recrystallization due to relatively high Mn content. The mechanical properties of the studied steel were evaluated by uniaxial tensile test at room temperature, and the detailed characterization of microstructural evolution was performed by scanning electron microscopy (SEM), electron backscatter diffraction (EBSD), transmission electron microscopy (TEM) and X-ray diffraction (XRD). The results show that the recrystallization process of the cold-rolled plates with 50% or 70% rolling reduction during ART annealing was effectively controlled, resulting in a desired mechanical behavior, i.e., high yield-to-tensile ratio, continuous yielding and outstanding combination of strength and ductility. This is because a certain proportion of deformed grains are retained due to incomplete recrystallization, which retains a higher density of mobile dislocation. This concept can be suggested to be quite suitable for the manufacturing of medium Mn steel using continuous annealing process, in which heating temperature and time can be controlled flexibly.