Microstructure and mechanical properties of pre-homogenized high-Mn steel processed by equal-channel angular pressing

Abstract

The grain refinement of high-Mn steels is effective in sustaining cryogenic environments by retaining high strength at low temperatures. Therefore, equal-channel angular pressing (ECAP) can be used to fabricate structured high-Mn steels for cryogenic applications, although the process may introduce heterogeneous hierarchical defect structures that influence their performance. In this study, we consider the effect of pre-homogenization on the microstructure and mechanical properties of multi-pass ECAP-treated high-Mn steels at room and cryogenic temperatures. By varying the processing temperature (400 and 900 ℃) and applying homogenizing pre-processing to the initial workpieces, ECAP can produce distinct microstructures with grain sizes ranging from 0.22 to 24.33 μm. Decreasing the grain size increases the excess free energy, leading to an increase in the stacking fault energy from 25.9 to 37.8 mJ/m2 at room temperature. As a result, the steel processed by ECAP at 400 ℃ exhibits a low twin volume fraction and reduced strain-hardening rate. However, at cryogenic temperatures, the stacking fault energy of high-Mn steel is reduced, which enhances the twin activity and martensitic transformation. The latter process stipulates a reduction in the elongation to failure owing to the intensified crack initiation in the martensite phase. Moreover, ECAP at 900 ℃ offers the best strength–ductility balance by achieving a high twin activity without excessive martensitic transformation. In conclusion, outstanding cryogenic mechanical properties can be achieved by implementing multi-pass ECAP at elevated temperatures on pre-homogenized high-Mn steels. This study offers a low-cost alternative to Ni-rich steels for industrial applications. © 2025 Elsevier Ltd