Strain dependence of retained austenite to martensite transformation in 13%Ni steel and numerical study of its effect on hydrogen diffusion

With the growing demand for large-capacity liquified hydrogen storage, 13 % Ni steel has emerged as a cost-effective material candidate due to its excellent cryogenic toughness. In this study, the martensitic transformation behavior of retained austenite under tensile and compressive deformation at 296 K, 77 K, and 20 K was quantified using in-situ neutron diffraction measurements. The results show that martensitic transformation is more pronounced under tensile and at lower temperatures, with nearly half of the retained austenite transforming at 20 K and 77 K at a plastic strain of ∼ 0.03. A quantitative relationship was established based on the strain dependence of retained austenite for subsequent modeling. Based on these results, a hydrogen diffusion model considering lattice, dislocation, retained austenite, and fresh martensite traps was established. Finite element simulations were conducted to investigate hydrogen distribution in crack tips under various initial retained austenite contents. The results indicate that the initial retained austenite content strongly influences hydrogen trapping and lattice hydrogen concentration near crack tips. Higher retained austenite content mitigates hydrogen diffusion, whereas lower content enhances hydrogen accumulation in regions of high hydrostatic stress, highlighting the critical role of retained austenite in suppressing hydrogen embrittlement in 13 % Ni steel.