Refining hydrogen-dislocation interaction model for thermally activated plasticity in Fe-Cr-Ni austenitic steels: Analyzing stress-dependent activation volume

Understanding the role of diffusible solute hydrogen (H) as an obstacle to dislocation glide is essential for elucidating the solid solution-hardening mechanisms induced by H in Fe-Cr-Ni austenitic steels and other face-centered cubic (FCC) alloys. In the present study, we address this issue through an effective use of classical stress relaxation tests with a relatively long duration (∼1000 s) at 295 K. A Type310S (Fe–24Cr–19Ni) austenitic stainless steel was examined after uniformly pre-charging ∼8500 at ppm H under a pressurized high-temperature gaseous H₂ environment. The activation volume, V ( i.e ., a material volume involved in an elementary obstacle-dislocation interaction), as a function of externally applied stress, was analyzed to probe the impact of H on thermally activated dislocation motion through a field of multiple obstacle types. A unified stress– V relationship was identified for both non- and H-charged specimens, in addition to an H-induced retardation of deformation kinetics under an equivalent stress level. These findings demonstrate that the primary obstacles to dislocation motion are alloying elements (and forest dislocations) even under the presence of H, with H contributing an additional activation barrier to overcome these inherent obstacle types.