Chemical composition dependence of the strength and ductility enhancement by solute hydrogen in Fe–Cr–Ni-based austenitic alloys

Tensile tests of five commercial Fe–Cr–Ni-based austenitic alloys were conducted after thermal hydrogen precharging in a pressurized gaseous environment. The divergence in Cr and Ni concentrations affected the hydrogen solubility significantly as well as the impacts of dissolved hydrogen on the mechanical performance of the alloy. Hydrogen solubility increased with increasing Cr content and Cr/Ni compositional ratio, bringing about an escalating solid-solution hardening with a magnitude of ≈ G/1000 (G: shear modulus) per atomic percent of solute hydrogen. Furthermore, hydrogen facilitated deformation twinning in alloys with relatively low stacking fault energy (lower Ni content), in which deformation twinning occurred even in a nonhydrogenated state. Augmenting the twin density enhanced the work-hardening capability at the later deformation stage, giving rise to the improvement of uniform elongation via retarded onset of plastic instability. Consolidating the experimental results and hitherto-understood hypothesis on the response to hydrogen of other austenitic materials, the essential conditions for promoting hydrogen-related strengthening and ductilization were deduced.