Research on health monitoring of extreme low-temperature equipment

Full-lifecycle health monitoring of extreme low-temperature equipment heavily depends on the stability of the cryogenic mechanical behavior of core structural materials. Notably, Fe-Mn-C series high-manganese steels stand as key candidate material for extreme low-temperature scenarios at 4.2 K. To address three critical challenges for this material system—i.e., the lack of 4.2 K constitutive models, multi-scale modeling bottlenecks, and insufficient local monitoring—that directly limit its health monitoring, this study targets Fe-22 wt% Mn-1 wt% C-0.3 wt% Cu high-manganese austenitic steel to systematically investigate its 4.2 K constitutive behavior and microscale deformation mechanisms. The results are as follows: (1) At 4.2 K, the material exhibits a serrated stress–strain response in the plastic stage, characterized by “variable period, amplitude, and equilibrium position”; this behavior is dominated by the synergy of low-frequency (<60 Hz) dynamic strain aging (DSA) and mechanical twinning. (2) 4.2 K-adapted cryogenic digital image correlation (DIC) technology reveals that the material exhibits differentiated strain distributions across temperature ranges, providing direct visual evidence for risk zone localization in health monitoring. (3) Microscopic characterization confirms that the hierarchical twin structure at 4.2 K is the core mechanism sustaining the material’s strength-plasticity balance; based on this, a correlation model linking “macroscopic strain distribution and microscopic twin evolution” is established. Leveraging these results, this study establishes a foundational 4.2 K constitutive model incorporating DSA-twinning coupling terms. This model enables quantitative support for “stress-strain-failure risk” analysis in extreme low-temperature equipment health monitoring, facilitating the advancement of monitoring systems from “macroscopic evaluation” to “precision early warning”.