5th International High Manganese Steel Conference - HMNS 2022

Medium-Mn steels (MMnS) with very low (≤ 0.05 wt.%) carbon content exhibit improved cold-formability but limited strength due to the deficient strain hardening. A combination of nano-precipitation and enhanced transformation-induced plasticity (TRIP) effect is a promising approach to improve the strength and ductility of such MMnS. In this study, a low-carbon (0.05 wt.%) medium-Mn steel (MMnS) containing Cu and Ni (1.5Cu1.5Ni-alloy) was developed to influence the austenite stability and to stimulate the nano-precipitation. A reference MMnS without Ni and Cu (0Cu0Ni-alloy) was used to elucidate the effect of Cu and Ni on the austenite reversion and nano-precipitation behavior. The alloying with Cu and Ni was beneficial for the austenite reversion during the proposed shortened annealing period, which is revealed by using synchrotron X-ray diffraction (SY-XRD). During the subsequent tempering, the RA fraction of 1.5Cu1.5Ni-alloy further increased to 38.5 vol.% and pronouncedly contributed to its strain hardening behavior through the TRIP effect. In contrast, the RA fraction of the reference alloy remained almost unchanged. The high number density of Cu-based nano-precipitates with a mean diameter of approximately 4 nm was observed in the ferrite phase of 1.5Cu1.5Ni-alloy using three-dimensional atom probe tomography (3D-APT) and significantly increased the yield strength. The current study demonstrates the beneficial influence of Cu and Ni on austenite reversion and nano-precipitation behavior, which subsequently enabled an enhanced strain hardening with increased ductility and a high level of yield and ultimate tensile strength, respectively.