Revealing the intrinsic nanohardness of retained austenite grain in a medium Mn steel with heterogeneous structure

The present work investigates the intrinsic nanohardness of retained austenite in medium Mn steel with heterogeneous structure. By increasing the austenite stability using Mn alloying, the martensitic transformation in both small and some large austenite grains is effectively suppressed during nanoindentation measurement. The average intrinsic nanohardness of small and large austenite grains are found to be 4.4 GPa and 5.5 GPa, respectively. The higher nanohardness of large austenite grains as compared to the small austenite grains is due to the higher dislocation density. Despite of grain boundary strengthening to the ferrite phase, the nanohardness of ferrite is still lower than that of small austenite grains. The intrinsic nanohardness of austenite in the present work could be used to generate valuable input parameters (i.e. yield strength, strain hardening) for the modeling work on high strength steels with retained austenite.

Automated summary

Increasing austenite stability through Mn alloying effectively suppresses martensitic transformation in medium Mn steel, resulting in higher nanohardness for large austenite grains. Despite grain boundary strengthening, the nanohardness of ferrite remains lower than that of austenite grains. The intrinsic nanohardness of austenite found in this study can provide valuable input parameters for modeling high strength steels with retained austenite.