Microstructure and mechanical properties of high-Mn-ODS steels

Abstract

The contribution of dislocation density to strength of Cr–Ni containing austenitic ODS steels is assumed to be limited by dynamic recovery during consolidation of mechanically alloyed powder [Seils et al. Materials Science and Engineering A 786 (2020) 139452]. In order to prevent the reduction in dislocation density by dislocation annihilation subsequent to thermally activated cross slip during recovery, Cr and Ni were replaced by 24 and 34 wt% of Mn in the present study. The comparably lower stacking fault energy leads to larger stacking fault widths and, hence, lower probability of cross slip. The Mn-ODS steels were successfully manufactured by mechanical alloying and subsequent field assisted sintering. X-ray diffraction analysis revealed increased dislocation densities for both Mn-ODS alloys compared to a previously reported Cr–Ni-ODS steel. Formation of additional ε-phase was observed in the lower Mn alloy. Compression and hardness tests confirmed an improved strength and hardness of the Mn-ODS steels. Less thermal stability was found compared to the Cr–Ni-ODS steels due to pronounced ripening of oxide particles as well as grain coarsening in both investigated alloys.