5th International High Manganese Steel Conference - HMNS 2022

The strength-ductility balance of steels is strongly dependent on their microstructure characteristic which dominates strain distribution, such as texture, grain morphology, and dispersed hard- and/or soft-phases. It is generally known that addition of Mn above 10% decreases stacking fault energy, which results in the occurrence of γ→ε→α’ martensitic transformation. The microstructure formed via γ→ε→α’ martensitic transformation exhibits ultra-fine microstructure containing retained ε martensite. This ultra-fine microstructure of matrix would inhibit non-uniform deformation, whereas the hard-phase of ε martensite probably would induce the strain localization. In this study, the combination of SEM observation and digital image correlation (DIC) method was carried out to investigate the effect of ultra-fine microstructure and ε martensite on the strain distribution in the duplex martensitic medium Mn steel. An as-quenched 10%Mn-0.1%C steel was used in this study, which was electrical discharge machined to the small tensile test piece. The tensile test was performed in a SEM (Sigma500, Zeiss) with maintaining the acceleration voltage of 2 kV. The strain distribution was analyzed by DIC software (VIC-2D, Correlated Solutions). The dominant microstructure of 10%Mn-0.1%C steel was found to be α’ martensite with the block size of 0.4±0.2 µm. The ε martensite and retained γ dispersed in the matrix exhibited granular-like morphology, whose grain size was below 2 μm. The DIC analysis revealed that strain localization tended to occur along the longitudinal of blocks rather than the ε martensite and/or retained γ. In the presentation, we will also discuss the difference of strain distribution between coarse martensite and ultra-fine martensite.