Thermally activated dislocation motion in hydrogen-alloyed Fe–Cr–Ni austenitic steel revisited via Haasen plot

Abstract

Enhancement of thermally activated dislocation motion by solute hydrogen (H) has been envisaged in Fe–Cr–Ni austenitic steel through accelerated stress relaxation and a prolonged creep duration. Nevertheless, differences in the imposed stress/strain between the compared non- and H-charged samples at the starts of these mechanical transients, as well as involvements of other obstacles (e.g., alloying elements and forest dislocations), mask the essential effects of H. We performed stress relaxation and strain rate jump tests at multiple stress/strain for Type310S austenitic steel with ∼7600 at ppm H at 296 K. The measured strain rate sensitivity (SRS) was evaluated via a methodology so-called Haasen plot. By screening the latent factors above, primary role of H was revisited: they work as short-range obstacles, hindering the dislocation movement. Multiple H atoms potentially participate in each thermal activation event, giving rise to a stress-equivalent activation volume and a proportionality between H concentration and yield strength.