Recognition of fracture stages of CHN01 austenitic stainless steel by acoustic emission at cryogenic temperature

In this study, the fracture behavior of CHN01 austenitic stainless steel at cryogenic temperature (77 K) was systematically investigated using an integrated approach combining mechanical testing and acoustic emission (AE) analysis. Tensile and fracture toughness tests were performed on solid solution heat-treated CHN01 specimens, revealing exceptional mechanical performance with a yield strength (Rp_0.2) of 1057 MPa, an ultimate tensile strength (R_m) of 1602 MPa, and a provisional fracture toughness (K_Q) of 201 MPa·m^1/2. Concurrently, AE signals recorded during fracture testing were analyzed using an optimized unsupervised k-means clustering algorithm. Two distinct AE signal clusters were identified, i.e. cluster 1, characterized by high-frequency, low-energy, and continuous features, which are associated with elastic microcracking; and cluster 2, exhibiting low-frequency, high-energy, and burst characteristics, indicative of plastic energy dissipation. Analysis of the AE data revealed that during the linear elastic deformation phase, 91.6 % of the recorded signals originated from cluster 1, while in the nonlinear phase, almost all AE signals were from cluster 1—suggesting that the energy released during crack propagation was predominantly absorbed by the evolving plastic zone. These findings underscore the potential of integrating AE monitoring with mechanical testing to provide robust, real-time insights into fracture processes at cryogenic temperatures, thereby offering valuable guidance for material selection, crack monitoring, and early warning in cryogenic applications such as high field superconducting magnets.