Hydrogen effects on the cyclic creep deformation mechanisms of 310s austenitic stainless steel

Hydrogen effects on cyclic plasticity of austenitic stainless steels represent a critical issue for fatigue design, as constitutive behavior is essential to assess both global and local mechanical responses of structures. In this work, the effect of solute hydrogen on cyclic hardening and cyclic creep deformation of AISI 310S, uncharged and hydrogen-charged (∼113 wppm), was investigated prior to crack initiation. To elucidate hydrogen–plasticity interactions under cyclic loading, a consistent mechanical database covering a range of mean stress σ m and maximum stress σ max levels was established under stress-controlled tension-compression ratcheting at 300 K (0.05 Hz) and compared with static creep. Internal stresses were quantified by partitioning the flow stress into back stress X and effective stress σ eff , and dislocation structures were characterized by quantitative TEM. The tensile plastic strain history, governed by σ max , reveals three deformation regimes, each distinctly affected by hydrogen. In Regime 0 (low σ max ), hydrogen promotes planar slip and homogeneous dislocation distributions, yielding high plastic strain reversibility and suppression of cyclic creep. Consistent with reduced stacking fault energy and inhibited cross slip, hydrogen increases the threshold stress σ th for the onset of cyclic creep. In Regime I (σ max > σ th ), the cyclic creep rate follows ln(dε r /dt) ≈ K(σ max /μ) + B, where μ is the shear modulus; hydrogen decreases the slope K, attributed to enhanced plastic strain reversibility and delayed formation of polarized dislocation walls. In Regime II (high σ max ), well-developed dislocation cell structures dominate, and the influence of hydrogen becomes less pronounced. Across Regimes I and II, the cyclic creep rate scales uniquely with the back-stress amplitude X a , independent of hydrogen content, indicating that fluctuations of long-range internal stresses govern ratcheting. This finding reflects the ability of cyclic loading to progressively destabilize the dislocation structure; hydrogen mitigates this effect primarily through enhanced short-range pinning.