Influence of microstructure on hydrogen trapping and diffusion in a pre-deformed TRIP steel. (8th February 2023) - Hempel, Christian
Abstract: Austenitic steels are known to exhibit a low hydrogen diffusion coefficient and hence a good resistance to hydrogen embrittlement. Therefore, it is an experimental challenge to investigate their hydrogen diffusion properties. In this study, the electrochemical permeation technique is used to determine the hydrogen diffusion coefficients in different pre-deformed states ( φ = 0, 0.32, 0.39, 0.49) of the high-alloy austenitic TRIP steel X3CrMnNiMoN17-8-4 in a temperature range of 323 K–353 K. In combination with microstructural analysis, a correlation between phase transformation from γ-austenite to α′-martensite and dislocation density is shown. As a result of the lattice transformation from fcc to bcc, the diffusion rate of hydrogen is significantly increased ( D app, φ = 0 = 3.6 × 10 −12 cm 2 s −1, D app, φ = 0.32 = 1.6 × 10 −11 cm 2 s −1 at 323 K). With higher degrees of deformation, the dislocation density also increased in the martensite islands, resulting in a degressive growth of the diffusion coefficient ( D app, φ = 0.39 = 5.3 × 10 −11 cm 2 s −1, D app, φ = 0.49 = 1.1 × 10 −10 cm 2 s −1 at 323 K). Moreover, detailed calculations are performed to describe the way of hydrogen trapping and to give a possible mechanism of diffusion. Graphical abstract: Image 1 Highlights: Diffusion coefficients of H in austenitic steel (e.g. D 323 K = 3.6 × 10 −12 cm 2 s −1 ). Accelerated hydrogen diffusion due to strain-induced α′-martensite formation. Amount of trapped hydrogen strongly decreases with increasing temperature. Solubility of hydrogen significantly decreases with increasing α′-martensite.