Evaluation of Hydrogen Embrittlement in Austenitic Stainless Steels during SSRT Using Acoustic Emission Method

Abstract

While the hydrogen embrittlement (HE) susceptibility of austenitic stainless steels is generally linked to austenite stability, the detailed mechanism during the actual deformation process is not fully understood. This study focuses on the characterization of hydrogen-induced damage progression by analyzing Acoustic Emission (AE) signals associated with discrete microstructural events, including strain-induced martensitic transformation and dislocation activity. Slow Strain Rate Tensile (SSRT) tests were conducted on AISI 304 using specimens pre-charged with high-pressure hydrogen gas. The detected AE signals were analyzed using waveform parameters, such as frequency spectra and amplitude distributions, in correlation with stress-strain behavior. To capture small AE events that are typically obscured by background noise in broadband monitoring, frequency band-splitting enhanced the S/N ratio. By comparing the AE characteristics of hydrogen-charged and uncharged specimens, the results reveal a unique trend where the Gutenberg-Richter b-value increases in hydrogen-charged specimens, contrary to typical brittle fracture. Furthermore, high-frequency AE events decreased in the hydrogen-charged material. This indicates that hydrogen intrusion suppresses the continuous progression of macroscopic martensitic transformation, which typically emits high-frequency signals, thereby shifting the dominant process to smaller-scale, localized events. These results provide clear insights into how hydrogen modifies the damage sequence and promotes embrittlement in austenitic stainless steels.