Abstract:

Deep cryogenic treatment (DCT) has emerged as a promising approach to enhance the
performance of high-manganese austenitic steels used in oil-sands mining, yet the fundamental
mechanism by which DCT alters stacking-fault structures and stacking-fault energy (SFE)
remains insufficiently resolved. In this work, we employ in-situ X-ray diffraction (XRD) to
quantitatively track the evolution of stacking faults, microstrain, and lattice parameter during
cryogenic exposure, and integrate these findings with strain-controlled compression testing to
directly correlate the XRD-derived SFE changes with deformation mechanisms, particularly
twinning activation. Using the Reed–Schramm methodology for SFE determination from
diffraction line broadening and peak shifts, in-situ XRD measurements captured the dynamic
evolution of the austenitic lattice throughout the DCT cycle. A progressive lattice contraction
was observed as the temperature decreased to −180 °C, accompanied by a significant reduction
in microstrain and dislocation density. These changes were reflected in both peak broadening and
systematic shifts in the {111} and {200} reflections, allowing precise calculation of stacking-
fault probability (SFP) and the corresponding SFE at each stage of the cryogenic cycle. The
results show a clear post-DCT reduction in effective SFE, indicating a lattice state more
susceptible to Shockley partial separation and fault-mediated deformation. To validate the
mechanical implications of the XRD findings, compression tests were performed on DCT-treated
and as-received specimens. The DCT material exhibited a distinct acceleration in twinning
kinetics, initiating mechanical twinning at lower strains and sustaining a higher rate of twin
propagation throughout deformation. This behavior is consistent with the lower SFE measured
by in-situ XRD, which reduces the critical stress required for twin nucleation. The enhanced twin
activity also resulted in a more pronounced Stage III hardening regime, confirming that the
lattice conditioning observed during DCT has direct consequences for subsequent plasticity. By
combining real-time XRD analysis with mechanical testing, this study provides a comprehensive
understanding of how DCT modifies the stacking-fault landscape and, in turn, controls the
activation and evolution of twinning in high-Mn steels. The integrated approach highlights the
value of in-situ XRD as a quantitative tool for assessing SFE evolution, while the mechanical
tests affirm the functional impact of these microstructural changes. These insights offer an
experimentally grounded pathway for tailoring cryogenic processing conditions to engineer high-
Mn steels with improved strain-hardening capacity and enhanced durability in extreme mining
environments.

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Dr. Dmitry Vrublevskiy