In situ neutron diffraction reveals the effect of Cu micro-alloying on low-temperature tensile properties of TWIP steels.

High manganese steels are emerging as promising structural materials for cryogenic applications due to their low production cost and great potential in achieving excellent strength-ductility combinations. Micro-alloying serves as a desirable method in tailoring stacking fault energy (SFE) of the steels and thus tailoring the mechanical performance. In this study, we investigated the dedicate role of Cu addition played on the mechanical and microstructural responses of high manganese steels at the low-temperature range (293, 173, and 77 K) via in situ neutron diffraction and microscope characterizations. The addition of 1 wt%Cu to the steel not only effectively improved the yield strength (YS) and elongation but also increased the SFE thus postponing the martensite formation. For both high Mn steels, as deformation temperature decreased, the tensile strength was increased linearly, the formation of stacking faults and dislocation was promoted, and the SFE almost linearly decreased with a slope of about 0.06 mJm−2·K−1. The contributions to YS and flow stress from lattice friction, grain boundary, dislocation, deformation twins, and phase transformation were determined based on neutron diffraction results and previously validated models. The work revealed the critical roles of Cu micro-alloying in tailoring the SFE of TWIP steels and the resulting deformation mechanisms, paving the way in adapting new high manganese steels for cryogenic applications. • Cryogenic mechanical properties of two TWIP steels were measured. • Stacking fault energy (SFE) was determined theoretically and experimentally. • Deforming mechanisms were studied at cryogenic temperatures. • Adding Cu can enhance yield strength, tailor SFE, and change deformation behaviors. • Strengthening effects from a variety of hardening mechanisms were determined. [ABSTRACT FROM AUTHOR]