Dislocation-pinning and dynamic strain-aging in hydrogen-alloyed Fe-Cr-Ni austenitic steel at sub-ambient temperatures

The interaction between solute hydrogen (H) and mobile dislocations in Fe-24Cr-19Ni mass% (Type310S) austenitic steel charged with 8500 atomic ppm H was investigated by stress relaxation tests conducted over the temperature range 213–295 K. At ambient condition, H atoms form solute atmospheres that can migrate coordinately with moving dislocations. In contrast, the reduced H diffusivity at lower temperatures progressively impedes dislocation motion, leading to dynamic strain aging (DSA) during the relaxation process, manifested as a retardation of thermally activated deformation. As a direct consequence of this dislocation-pinning effect, a pronounced yield point emerged upon reloading after relaxation. The kinetics of solute atmosphere formation and DSA were further quantified by evaluating the exhaustion rate of mobile dislocation density as a function of relaxation time. The experimental trends were successfully described using a classical Cottrell atmosphere model based on size-misfit interaction, demonstrating that the fundamental role of H in governing dislocation mobility is essentially analogous to that of other interstitial solute elements.