Distinct impacts of hydrogen and carbon on thermally activated dislocation motion in Fe-Cr-Ni austenitic steel

Plastic flow behavior and strain rate sensitivity, S , of Fe-15Cr-15Ni (mass%) austenitic steel, alloyed with either hydrogen or carbon, were evaluated by tensile and stress relaxation tests at ambient temperature. The effects of these two interstitial elements on solid solution-hardening and thermally activated dislocation motion were compared in terms of Haasen plot — S versus flow stress. Both hydrogen and carbon exhibited solid solution-hardening of the same order of magnitude, increasing S proportionally with their concentrations. However, their ability to increase S was distinct. Hydrogen caused a much steeper increase in S , acting as extremely localized obstacles resisting dislocation motion. In contrast, despite exhibiting comparable solid solution-hardening, carbon led to an order of magnitude smaller increase in S than hydrogen. This result demonstrates a relatively long-range and less rate-sensitive nature of carbon, which is totally different from hydrogen in its obstacle character.