Strain Aging Behavior of an Austenitic High‐Mn Steel

Abstract

The bake hardening treatment shows great potential for increasing the yield strength of steel components for automotive applications. This study investigates the effects of bake hardening on the yield strength and ductility of an austenitic high‐Mn steel. In order to identify a promising process window, the prestrain, the bake hardening temperature, and the annealing time are varied. The bake hardening effect is evaluated by the uniaxial tensile tests with digital image correlation (DIC) in situ monitoring. The results show strong bake hardening effect on the high‐Mn steel when certain amount of prestrain is applied. Large amounts of prestrain even leads to room temperature aging. Small angle neutron scattering (SANS) measurements indicate the absence of Mn–C short range ordering (SRO) after the prestrain; however, the nano‐sized Mn–C SRO re‐occurs after the annealing. At high prestrain degree, an increase in the number density of the Mn–C SRO is found in both cases, after annealing at elevated temperature and aging at room temperature, indicating an accelerated Mn–C SRO formation. The results suggest that SRO is responsible for an increase in the yield strength and a pronounced yielding of the high‐Mn steel after bake hardening treatment.