Hydrogen embrittlement in low-Ni austenitic stainless steel: Microstructure-driven mechanisms revealed by experimental and simulation study

The present study investigated the microstructure-driven mechanisms governing hydrogen embrittlement (HE) in low-Ni austenitic stainless steels, by integrating multi-scale experimental analysis with crystal plasticity and hydrogen transport simulations. The results revealed that while α’ martensite increases susceptibility to HE, grain-size heterogeneity and intragranular nanoscale carbides play critical roles in local H distribution and H-induced cracking. Grain refinement enhanced strength and decreased H uptake; however , simulations demonstrated that inevitable grain-size deviations induced stress heterogeneity between fine and coarse grains. H segregation along high-angle grain boundaries, coupled with stress heterogeneity, promoted localized H-induced cracking in highly deformed regions to deteriorate HE resistance. Increased carbon content for strengthening facilitated the precipitation of nanoscale Cr 23 C 6 carbides within austenite grains, but these carbides increased the uptake of diffusible H. Their interfaces acted as preferential crack initiation sites in central regions, and the cracks propagated toward the surface during deformation. Surface H-induced cracks generated additional stress concentrations in the interior, which synergized negatively with central cracking to accelerate premature fracture of the steel. • Experiment coupled with simulation revealed mechanism of hydrogen embrittlement. • Grain refinement decreased H uptake, but grain size heterogeneity was detrimental. • Stress heterogeneity and H segregation jointly promoted localized cracking. • Intragranular carbides increased diffusible H uptake and acted as cracking sites. • Surface H cracks synergized with central carbide cracks, causing premature fracture.